Cropping a photo hangs Photos app on my Mac Mini

How much free space do you have on your boot drive?

How much memory do you have?

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?

Try the following: launch Photos with the Option key held down and create a new, empty library. Import a couple of photos to it and test the crop function, If it crops without a problem close the text library and open your current library and test the crop function there.

Can you answer Old Toad's questions?

How much free space do you have on your boot drive?

System Settings>General>Storage. Mine says 1.6 TB used of 2 TB. What does yours say? Apple recommends having at least 10% free storage.

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?

 To narrow things down, try these steps:

• 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 

• You tried this, right? 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.  This is a bit harder, because a new user can't access a different user's stuff. You would need to move your Library out of your own user's folder up to the general "Users" folder. 
• Rebuild your Photos Library--close Photos and re-launch by option-command-clicking the app icon. If you use iCloud Photos, it’s possible that this will cause a re-sync that lasts long enough to make you nervous.

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…

JimFerguson wrote:

I spoke too soon. The problem is back

Please download and run Etrecheck.  The free version is sufficient.

Copy and paste the results into your reply. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and after clicking on the Reply button use the Additional Text button to paste the report in your reply.

Check Etrecheck's Privacy settings and make sure the checkbox for full disk access before running:

Then we can examine the report and see if we can determine the cause of the problem.

[Edited by Moderator]