What happened with my PC's BIOS?

Gee, I guess it’s too late to ask for direction before you took this drastic step. To state the obvious. Assuming Garuda left may have left an efistub, efivarfs is where I would start reading.

Also assuming I don’t have a clue–and I don’t–what Garuda is using as a bootloader or what bootloader errors are current, or login manager (did I just see lxdm?), I would also start a search similar to that.

You didn’t give us even a clue as to which version of Garuda you were using, and you ignored the required garuda-inxi output (do it from a live ISO).

Minimal effort on your part may result with minimal effort on the part of people who might otherwise help you. You haven’t given them enough information.