When using doing nixos-rebuild and using Limine as the bootloader, the rebuild fails because Limine fails to override the EFI boot entry due to it already existing.
The command that is attempted to run during the rebuild, with the corresponding error, is:
❯ efibootmgr -c -b 0001 -d /dev/nvme0n1 -p 1 -l \\efi\\limine\\BOOTX64.EFI -L Limine -o 0001,2002,3001,2001,2004
efibootmgr: ** Warning ** : Boot0001 has same label Limine
efibootmgr: Cannot create Boot0001: already exists.
There shouldn't be any notable differences between the boot setup on barbatos compared to on calibarn, and when barbatos used to use GRUB this wasn't an issue.