Gigabyte Z690 UD

Pros

• I tried for a bit with a few different versions before searching forums/youtube for info on the board and found multiple people saying that for this specific board you have to flash using the button rather than the interface.
• If you can already boot to BIOS already there is no reason to be using the USB flashback feature.
• I personally use a 2gb formatted to fat32, and I've never had issues on any board even using flashback.
• Then I would update it from the BIOS directly instead of using Flashback. You don't need to rename the file. Just use the file unmodified. Make sure it's the right version of the motherboard

Cons

• I've tried with USB 2 and 3, tried with 32 and 16 gb size sticks, tried to update it in stages with older BIOS updates first. Nothing has worked.
• I know the board is reading it because I can boot to the UEFI just fine and try to update the BIOS that way. Though it hits a check error every time as I read I should expect.
• The check error usually means you are trying to load a BIOS file that is not matched to the motherboard. Some boards have a DDR4 and DDR5 version, make sure you didn't mix them up.