Getting Unknown Error (3) when exporting Photos edited using Clean Up function to external hard disk

ExFAT isn't native to Mac, but it usually works OK if files are not too complex. Jpeg files should be fine, for instance. But f the drive doesn't have to be shared with other OSs (like Windows,) then it's best to use APFS. Never try to run a Photos library from ExFAT!

What's happening is weird, and as I said, it doesn't behave that way for me. There could be other problems. You should try these things to narrow things down:

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

           Start up your Mac in safe mode - Apple Support 

Those are the easiest things to try first. Then try these:

• 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.
• Make a new user and see if the same problem recurs with it
• 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.

Let us know what happens…:

jadelyn_loey wrote: I've photos edited using Clean Up function in my iPhone 15 Pro Max (iOS 18.1.1). I imported these photos from my iPhone into Photo app in my Macbook Pro.

When I tried to export these edited photo to the external hard disk, I encountered the Unknown Error (3) and fail to export. …

Am I understanding correctly that they export to your internal drive just fine? And you tried File>Export>Export Unmodified Originals and that worked OK, but File>Export>Export nn Photos did not?

I just tried using Clean Up on my iPad, syncing it through iCloud Photos, and then exporting to both my internal drive and an external drive with no problems. My external drive is formatted APFS-- how is yours formatted?

I also just tried erasing something else from the same picture with my iPhone rather than the iPad, and it worked the same. However, if I keep doing this, there won't be much left in the picture!