I tried out CandleFlicker, changing UPDATE_RATE to 450 as TK suggested. It still looks like a candle, but it’s a different feel than Candle Mode from Andúril. I ended up putting it on a 2 x 7135 driver in a Convoy S2+ host, and I ran it both ceiling-bounced and with a diffuser. Even on 2 x 7135, it was far too bright to use a like a real candle in a dim room; I missed the adjustable brightness that Andúril provides.
Given all the limitations of using an ATtiny13A for something like this, I decided this was an excuse to buy another flashlight for this purpose. I just got an Emisar D4 (my first one, I am behind the times) and a new quad board with 3000K Nichia 219Cs. Now I just need to figure out why the driver won’t come out to let me flash Andúril.