IIRC Windows 11 will no longer boot from MBR partitions & you have to convert them to GPT.
Re:Fedora considers deprecating legacy BIOS
by little_panda on Thursday April 21, 2022 @04:14PM
(#31114638)
It will; there are tweaks out there that explicitly allow for installing windows 11 on an mbr partition.
Hint: download the latest version of Rufus, point it to a windows 11 iso and select the "Extended installation" mode. The result will happily install itself onto an MBR partition.
I performed an upgrade (!) of a windows 10 installation to windows 11 in this manner; I'm writing from this SSD right now.
PS C:\Users\alexa> $(get-disk | ? {$_.IsSystem}).PartitionStyle; [System.Environment]::OSVersion.Version
MBR
Major Minor Build Revision
----- ----- ----- --------
10 0 22000 0
Viceversa, it is possible with some loaders to boot BIOS from GPT (not easy-peasy or straightforward but it can be done).
As well, the FAT is only a requisite if there is not an EFI driver for the filesystem, as an example some motherboards and RUFUS provide a NTFS driver that allows booting from NTFS volumes under UEFI.
Still, while in theory GPT and UEFI have a few advantages, there is not in practice (yet) any meaningful reason to remove support to BIOS, though lately a number of notebooks have UEFI firmware only (no CSM aka BIOS), I cannot see how removing an option/choice from a distro can be a good thing.