thanks for the heads up. Unfortunately I'm without macOS as my motherboard died (see my updates section). The only thing that I can update on this build is the EFI because the tools to do that all work in Linux which is my temporary Desktop PC for the time being (a re-purposed Mini PC meant for a OPNsense firewall) well, I had to improvise
I had almost same experience with GA-H77M-D3H. The reboots after changing hardware and clean. reset CMOS. Also was thinking my PSU had broken down. I almost gave up, but did not trust the bios and backup BIOS. Bought CH341A BIOS programmer and used my LINUX machine to reprogram BIOS (had to de-solder one of the BIOS chips) Since then it all works like a charm again. So if you still have the board....
I'm still on Catalina, but I'm going to try my luck to upgrade to Big Sur now with the help of your guide.
thanks 4soulshine, glad you liked the guide, funnily enough, I did buy the the CH341A Bios programmer in August and used a few Linux guides like this Lonnie Mason guide, Jens Depuydt's guide and deftdawg's YouTube but i had no luck with it. I think that i tried it so many times that I wore out the clip which will no longer seat the BIOS chip properly. I might as a last resort buy a new BIOS chip before ditching the board.