I have a UEFI system right here under my desk that provides legacy BIOS services for running option ROMs, video cards, SCSI host bus adapters, network adapters, anything. It even scans out their legacy video outputs in a little window. There's nothing incompatible between UEFI and legacy option ROMs. Perhaps you are thinking of Secure Boot.
Nope. I think there must be a miscommunication here so I'll be more explicit.
If you have CSM/BIOS mode on your UEFI default motherboard and you set it to CMB/BIOS mode of course you can run BIOS based video cards.
But if you switch your mobo to UEFI boot (say, because you want to run future Fedora, or maybe boot off an nvme storage device) you can't use your BIOS firmware video cards (unless, like some gigabyte cards they shipped for a few years with both BIOS firmware and UEFI firmware). It has nothing to do with secureboot or signing or any of that. GPU's are intimitely involved (INT_10h in BIOS and something cursed in UEFI GOP) in the first few operations on boot in both systems and the firmware on the GPU has to be able to fulfill that role.
So Fedora removing BIOS boot effectively removes the ability to use most video cards ever made. Anything designed before 2015 has a decent chance of causing trouble.
Actually you can, you just don't get firmware boot support. Plenty of those boards work just fine in linux/etc because they reprogram the entire board using AtomBios/etc when the ati/nouveau/etc drivers load. The Arm/PPC/riscv people are all running the same PCIe boards as everyone else, and outside of a few cases they are doing just fine not running the x86 option roms.
A lot of firmware supports using CSM to do GPU init and then providing UEFI interfaces on top of that. Of course, this is incompatible with Secure Boot.
In fact, you can't really run any other legacy option ROMs without legacy VGA support. You can run legacy SAS option ROMs for example and still do UEFI boot because of similar support for Int13, but to even run them require VGA text mode to be working.
