Thanks, TheTank20,
You are quite right. Win11 won't install if it doesn't have complete control over its EFI, reserve, and recovery partitions, as well as its own C:\ partition. So best thing to do if you are reinstalling Win11 is delete all Win11 partitions, including the EFI (ESP) partition, make them "unallocated", and then reinstall Win11. If you are dual booting Linux, you then have to reinstall the EFI entries into /boot/efi/EFI/fedora (or whatever). If anybody needs help with the latter, just let me know.