"iCloud Photos is only available on macOS Standard, macOS Extended and APFS formatted volumes"
I have a mac Photo library on an external drive that I wish to sync to iCloud. When I try to tick the box beside "Photos" to enable this I get the above error message.
I've tried rebooting in recovery mode and running First Aid on both the external drive and my hard drive, to no avail.
MacBook Pro 13″, macOS 12.7