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
What is the current format of the external drive?
You can use Disk Utility to view the format. Also see: Erase and reformat a storage device in Disk Utility on Mac - Apple Support
Be sure to note that reformatting will completely erase the drive.
Also note the following from Move your Photos library to save space on your Mac - Apple Support
Make sure that your external storage device, such as a USB drive or Thunderbolt drive, is formatted for Mac: either APFS format or Mac OS Extended (Journaled) format.
You can't store your library on a storage device used for Time Machine backups. And to avoid possible data loss, don't store your library on a removable storage device like an SD card or USB flash drive, or on a device shared over your network or the internet, including over a cloud-based storage service.
What is the current format of the external drive?
You can use Disk Utility to view the format. Also see: Erase and reformat a storage device in Disk Utility on Mac - Apple Support
Be sure to note that reformatting will completely erase the drive.
Also note the following from Move your Photos library to save space on your Mac - Apple Support
Make sure that your external storage device, such as a USB drive or Thunderbolt drive, is formatted for Mac: either APFS format or Mac OS Extended (Journaled) format.
You can't store your library on a storage device used for Time Machine backups. And to avoid possible data loss, don't store your library on a removable storage device like an SD card or USB flash drive, or on a device shared over your network or the internet, including over a cloud-based storage service.
"iCloud Photos is only available on macOS Standard, macOS Extended and APFS formatted volumes"
