Basically I had to reinstall Windows, but since the Windows Installer saw an EFI partition lying around, it decided it was a great idea to use it instead of creating a new partition.
Anyway, I need to recover the bootloader for Bluefin. What do I need to do?
From there, I think I would be able to create an EFI partition for Windows 11, separate from the one used by from Bluefin.
The entirety of the EFI partition seems stereotypical across installations with the exception of 1 file. You can install bluefin in a VM, grab the EFI partition, edit EFI://EFI/fedora/bootuuid.cfg to reflect the UUID of the 1Gb ext4 boot partition that should still be on your drive, and drop in and it should work fine. You can get the partition UUID from a partition manager or by booting a GParted LiveUSB.
The problem is that this will continue to happen. 2 EFI partitions on 1 drive isn’t the most stable config of all. If you’re set on this, make backups.
Welp, I just reinstalled Bluefin but using the Blivet-GUI, used some empty subvolumes, and then swapped the subvolumes on /etc/fstab for the previous ones.