You seem to be willing to do extensive research and reading on lights, but don’t appear to have done any reading on the battery links at all.
That’s a bit like reading about and studying new cars, really wanting one, but unwilling to learn to drive….because it’s too hard.
You have been led to the water. Take a drink.
Basically you can think of cells in two groups as far as "matching" one to a light...and really that's not often a huge issue with decent cells.
Low/Standard drain: These cells have magic jelly inside that gives them a higher mAh rating so they store more juice and can give longer run times, apples to apples. The tradeoff is that they can only handle so much heat (current draw) and these days that's usually at least 8 amps or so, and the vast majority of lights are still in the 1.5 to 6 amp range, so these cells are just fine. If you put a standard cell like this into a powerhouse light that pulls 10 amps or whatever, then at a minimum there's going to be so much heat buildup and performance loss that you'll be unhappy...and there may be other issues with the battery itself or the components on the driver, etc, maybe even the springs in the light.
High drain: The magic jelly in these is slightly different and allows them to withstand the heat of much higher currents running through them, but their tradeoff is that they don't store as much, so even with lower currents they have shorter run times. These will generally be at least a 15 amp rating but can be double that or more. We talk about those ratings with their "continuous drain" rating...what they can run at all the time and be happy. They also have a "pulse rating", which is much higher and meant to convey what they can handle for brief bursts, like turbo mode or vaping or a "max" setting on a vacuum, etc. You can put a high drain cell in any normal lower performing light, you'll just have shorter run times.
Then you can have added protection circuits to any of these cells. Generally not necessary - if your light doesn't have any protection built in to the electronics then you just don't pull an oops and leave the thing turned on unattended to where the battery drains alllll the way down. Otherwise you're good. These protection circuits (can be read about and seen in photos in the above links) are tacked on to the standard as-manufactured cell by the companies that sell them. Usually a tiny circuit board on the negative end, a conductor that runs up the side to the positive end, and another cap there...then it's all sealed up in a second plastic shrink wrap on top of the original manufacturer's shrink wrap. Depending on the maker and the cell size/circuit choice, this added protection extends the cell length by 3mm-8mm or so. Sometimes that added length is a problem for some light designs and you have to use plain normal factory cells in those (or explore modding avenues to let longer cells fit). The current drain on protected cells is almost always lower than the factory cells...again, that just depends on things, and these days the current rating for some protected cells is a lot higher than it used to be, which is great if you want protection for whatever reason. They also cost more and you're limited in choices.
So unless you have a high drain light that's really pushing the lumens for the included components, standard cells will often be a fine choice. If your light needs high drain cells, then pick up a couple for the collection. I would stay away from the cells with on-board charging. I've only had a few of them and they're so-so, but all of them had lower mAh and two of them failed (charging circuit...cell was ok). To make room for the charging components you necessarily have to reduce the height of the cell if you want to stay in standard dimensions...thus less magic jelly inside to work with. They can be convenient, though, and in emergency times you can just use some other juice pack to charge them up whereas a normal charger will require electricity (unless it will take a 12v DC car adapter).
So...look at the specs for the light(s) you want and look up reviews here that provide real life testing with numbers. If it turns out your light wants 10 amps then be sure you have a cell that will deliver, and if it's a normal just-a-few-amps light then you're good with whatever.
Excellent CRC, keep it up. 
I'm sorry that you got scared, but maybe you'll feel better as time passes.
If you decide to come back sometime, you're always welcome here, CRC. 
(And I don't think that you wasted our time.)
...
Although Li-Ion cells are really liked around here, you could just stick to AA and AAA flashlights.
Be sure to get some Eneloops, and you can still be a flashaholic. 
CRC…. If I may ask, how old are you??
Hey, at least you know how to use the internet and you found BLF.
That takes some brains.
I also have anxiety and depression, and am mentally disabled.
I have very few responsibilities in life, and I like it that way.
Plus, I'm pretty antisocial in real life, so we have some things in common.
Better toss out your cellphone(s), earbugs, mp3 players, everything else that has a Li cell in it, then.
I hope you realize you are freaking out over a possible but pretty rare occurrence? I’ve been using these batteries for a long time, unfortunately dropped many, and have created no disasters.
Statistically the most dangerous place in your life is your house……
Knowing that are you going to move out?
If you like the light, but are now genuinely afraid of lithium batteries, switch over to NiMh. They are generally considered safer, and you can still get some serious light out of them. How much light do you really need if you aren’t prowling the streets or woods after dark.
Note-you’ll find people that will tell you that NiMh have dangers too. Being alive has dangers. You gotta weigh the acceptable and reasonable from the excessive. That decision is always personal.
BTW - I appreciate your candor. I think more of you for opening yourself up, not less.
It was certainly difficult to do so, but it actually helps to know where you are really coming from.
And don't beat yourself up so badly about school or learning...seriously, those aren't indicators of your actual abilities! It's a little harder today maybe without college degrees and such but there are PLENTY of people who start out adult life in the same way(s) and go on to be happy and successful one way or another. Some people don't settle into their groove until they're in their 40s or 50s. And the yardstick by which society tends to measure "success" isn't always very accurate or fair, anyway...that's the truth.
Also...your now-flickering light. I think I said this in another comment here, but that tells you something got knocked out of whack with the impact, so somewhere in there electricity is not getting solid connection. There's no way to say what it is exactly without digging into the nitty gritty and trying to diagnose it. It could be as simple as needing to tighten a retaining ring in the head or tail, or it could be a broken solder joint or some other thing. Most of our lights are not "potted", which is when they cover the electronics and fill up space with rubber goop (which has advantages - like impact protection - and disadvantages), so harsh impacts tend to have consequences beyond just dinging up the aluminum housing...it's a crap shoot after a good drop. Disappointing but nothing to worry about with safety.
Want to learn more about batteries, good brands, how they work, and what NOT to do? Start watching and reading everything Mooch puts out. Ive been a patreon for a bit, best $1 a month i spend. HKJ here on BLF is Awesome too!
18650 battery dissection & explanation:
https://www.youtube.com/watch?v=V3-V00nhtpE
Yes, but there was a time where you didn't understand the risks of those things, either...so you learned, just as you are now with something different. It's all totally normal...and prudent, which is a good thing that you're showing here.
Really the risks are pretty small, but they aren't zero, and we're dealing with more packed energy than an alkaline or a watch battery, so respect and caution is good but I think as more of all these particulars sink in for you, you'll find that there's no reason to be scared. Don't go putting a cell in a vise or driving nails through them, and if you ever get a light that uses more than one cell, do observe the minor cautions there about discharge limits and not mixing cell types and whatnot, but overall with normal use and care, no worries. And a lot of our best-practice rules with cells have as much to do with getting the most life/most power from them, too, not just any inherent risks.
Dropping isn't usually unsafe at all, just the risk of making the light not work. With most lights the host provides more than enough protection for the cells and unless it's a really hard impact directly on one end the spring(s) are usually enough to cushion the cells from taking damage that way although it's possible that they could get dented or the driver in the head could get cracked/damaged in some way. With the low voltages we deal with here, flickering electronics aren't really a safety issue but I suppose with some designs there would be the potential for a short to cause unregulated current to flow...which would mean heat output...not so good for pockets or inside of backpacks or possibly the electric components with high powered lights. Like with some recent ones people had buttons stick in the on position or poorly made LED connecting wires that let the light run free...not from a drop but the same results essentially.
Now...if you drop a battery and it gets damaged from the impact, then some caution is prudent. The metal cans they are made from are quite thin, so they're easy to dent, and if that dent is deep enough it can push together the layers (jelly roll) inside and possibly cause a short, which would make the cell heat up, probably vent a little gas from the positive end, and hopefully not any worse (usually not any worse). In the CPF thread you linked (again, different type of battery there) he said the positive end of the battery hit hard and dented. Since that area is where + and - meet close together, there's a lot of potential for an accidental short to occur. There's a thin rubber gasket that separates the + and - in addition to the plastic wrapper on the cell that provides some insulation/separation. If the metal were crushed so much as to make the two meet, then you get a short. Or it could crush inwards and damage the CID protection foil or just separate the + end from its crimp, exposing the guts to oxygen. Again, usually a small risk/effect, but it's there. This is largely true for NiMH and NiCd cells, too, even silver oxide cells, but we just pack more punch into lithium-ion cells. So try not to drop cells and if you do, let them sit for a second before picking them up, and then inspect them for damage. Little dents are often just fine (and in fact, some lights will dent the ends of cells just from normal use if they're just a tad too long for its design). If the wrapper got torn, it's easy and smart to change that and you can buy wrappers super cheap, just takes a couple minutes to do that. If the cell starts to get warm or hot after a drop, chuck it outdoors onto concrete or something, just in case, but you're not usually going to see that. Again, if a light is dropped then the cell(s) inside are normally not at risk.
The everyday products you mention still have risk, too, of course. I'm sure you've seen many news stories over the years of laptops or scooters or juice packs erupting in flame or melting the devices. Most of those these days are a different lithium type but there are still several. Basically it's the same things happening where impact may cause a short...although shoddy electrical designs cause a lot of that as well, and even devices with built in protection circuits of varying types are not totally immune from risks...the combination of engineering and protections just minimize them to where hopefully it's just accident/abuse that causes problems.
For me, long ago I just adopted a policy of caution and observation - respect - for anything battery powered. I once pried open a tiny LR44 silver oxide watch battery just to see what was in there. Black dirt, basically...not so exciting. I put it in the trash can and moments later was headed out the front door to go do something. I smelled something...smelled like burning paper...and I'll be damned but the little opened battery in the trash can had gotten so hot with exposure to oxygen that it began to burn the paper towel that it was wrapped in! Glad I caught that before I left. Avoidable? Totally. Between that and some oopses while disassembling lithium battery packs and the many many stories of battery accidents over the years, I just pay attention now in how I handle them, stay present when recharging them, etc, etc. It's easy and while maybe not necessary or sometimes a slight hassle, it's prudent just in case. No fear, just a healthy respect (although I probably should have been afraid in the past, seeing as though I acted pretty boldly at times....). :)
Venting only happens when something goes really wrong, like serious physical damage to the cell or a direct shortcircuit, just dropping a good quality cell shouldn’t cause it to vent unless it’s from a tenth floor or something like that.
CRC - there has been a lot of useful info in this thread for you, but my 2 cents as someone who was VERY new and uneducated about this hobby only last year -
Overall - the way i learned and see others learning here is to follow this process (when in doubt):
I think this process works best because you are only learning what you NEED TO KNOW. and after awhile, your cumulative knowledge will be much more than you ever expected. I see members all the time starting threads just to ask a question, I don't know how its taken by the community - but i think its smart. if you cannot find your answer by searching, and feel overwhelmed by searching, just cut right to the chase and ask in a new thread.
Noctigon KR4
-I have a KR4, its one of my most carried lights, i drop it ALL THE TIME, no problems in my experience. it sits next to my head on my nightstand too.
-Use these batteries with it: https://www.18650batterystore.com/collections/molicel-18650-batteries/products/molicel-p26a and these https://www.18650batterystore.com/collections/18350-batteries/products/epoch-18350-battery-1100mah
-they're cheap, and reputable, and can handle the KR4. I use them both.
-Buy your batteries here : https://www.18650batterystore.com/ or here: https://liionwholesale.com/ and i think many of us could agree you will never get a junk battery. feel safe about that. thats half the problem, buying junk batteries. and if either of these places started to sell junk, you would here about it on BLF first. (There are other places to buy them, but i'm trying to make it straight forward).
-Buy a good charger, charge your batteries with it. this one is good: https://www.18650batterystore.com/products/xtar-vc4s
-There are many other good chargers, but i'm making this straightforward, and i think many here would agree about the charger.
It should only vent when there is pressure built up inside the sealed cell. That of course comes from heat, one way or another, or crushing physical force. Most cells and any that are approved for import into the US have a current interrupting device (CID) built into the top end of the cell...it's basically like a foil cover that ruptures (hopefully) when it should to prevent further heat/pressure/current flow. It's hard to see it and not so obvious if you don't know it's in there, but with most cells you can peer into the cutouts in the positive cap and see it down there. This is also why you shouldn't poke things into those cutouts or attempt to pry up/repair a positive end that has been dented. We aren't getting overly toxic fumes here like with those primaries or cells that are super heated, etc., but if a cell ever vents from an accidental short or damage, you may hear a little "poof" if you're close to it and listening, maybe catch a little odor. Again, don't huff it, but it's not the same as that other thread and not a huge concern. By the way, this kind of thing is why it's always a bad idea to carry extra cells in a pocket with keys or other conductive things, or pokey things, even if the cell is in one of those little silicone stretchy covers (which are otherwise handy but less protective than a plastic box or something).
This is the "unseen" protective device in a cell...and I guess, still, some ultra cheap suspect crappy cells don't incorporate it, but most do, and all the big makers do. Just a standard part of their construction. When you buy a "protected" battery, that's different - that is additional stuff added on to the outside of the cell (beneath the wrapper) with teeny electronics that cut the circuit based on voltage levels or heat.
You're welcome...don't give up, you're halfway there already. :)
Speaking of CRC, did anyone play River City Ransom (RCR) on the original Nintendo?
It was my favorite co-op 2-player game on the system.
Hey, better for you to be hot than, say, your batteries. :)