The following stuff is advertised as UPS, besides being a DIY power bank meant to provide power for up to 65 W laptops:

https://www.aliexpress.com/item/4000268838287.html

Battery arrangement is 3S2P, but if I were to buy one I'd make windows on the cover and install more batteries (of course all soldered or spot welded).

There are some related videos out there.