Hello again.
I was unable to flash to UEFI, the Q-Flash utility Gigabyte wants you to use refused to accept the file saying BIOS checksum error or something along those lines. However, I was originally on F9 and updated to F12 (the most recent non-UEFI version) and did not see improvement. Since you’re on F10, I think we can rule out a compatibility issue.

I did however get the screen to go away, but it is more of a Microsoft approach. Under Advanced in the BIOS settings you can disable Fullscreen LOGO. It’ll give you the text based POST instead and there is no graphical glitch.

Sadly, I am highly doubtful that would help with your other issues. Sorry this was of no use, if I manage to get to UEFI I will let you know what the outcome is. I believe it is possible with a DOS bootable USB drive, but I’ve not personally tried yet.