Weird problem with Retouch/Clean Up in Apple Photos

You wrote "When I try to retouch a photo, after option-clicking to select the source"

Are you trying to use the clone tool for retouching? The option-click to select and clone a source is no longer mentioned in the Photos User Guide since macOS 15.1. Perhaps it is no longer supported. Can you retouch your photos by brushing the the offending blemishes, but with option click?

See: Remove distractions and imperfections from your photos on Mac - Apple Support (EG)

I have a Silicon Mac Mini M4 and also don't get that black thumbnail when I use Clean Up on a photo.

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and test to see if the problem persists. Reboot normally and test again.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

How much free space do you have? Apple recommends at least 10% of the hard drive remain free. Less free space can cause weird effects.

Nice rainbow! I can see a faint double…

léonie wrote: … The option-click … it is no longer supported.

Option-click to Retouch does something, but it certainly isn't cloning. The "source" point moves around like it's copying, but I don't see any connection between it and the result. And nothing at the "source" point changes for me.

I'd like to have cloning…

Clean Up uses AI and isn't available on an intel Mac. Instead, as your picture shows, you have Retouch with the Adjust tools.

I don't get the postage stamp on my M3 MacBook.

Sorry for the typo. I meant to write "Can you retouch your photos by brushing the offending blemishes, but without the option click?"

Me too!