"Unable to save changes" error in Apple photos for Mac

Try these things:

• Restart the computer (of course)
• Re-start in Safe Mode. This bypasses certain potentially disruptive processes. Safe Mode is different for different computers, so see this: 

Start up your Mac in safe mode - Apple Support 

• Make a new user and see if the same problem recurs with it
• Use another library if you have one, or make a small test Library with a few pictures in it and see if the same thing happens. You can create a new Library by closing Photos and then option-clicking on the Photos icon.
• Rebuild your Photos Library--close Photos and re-launch by option-command-clicking the app icon.

The idea is to find out if the problem is with the Library, with your account, or with caches and login items, and stuff like that. One of these steps may fix the problem, but their failure to work also helps figure out what's happening.

Hello,

I am facing the same problem after the update to Sequoia.

The workaround that I am using that has solved the problem for me is to convert the pictures to JPEG using the built-in utility in the finder before the import to photos app.

I select all the pictures in the folder, right click, quick actions, convert image, convert to JPEG.

If I import to the photos app the converted files (virtually equal to the original ones) everything works fine for me.

Maybe this workaround can fix the problem also for you while we wait for updates.