Can't copy folder icons in Finder any more
Somehow, I have lost the ability to copy folder icons in the Finder. I use folder icons to easily recognize different locations, and I have a collection of icons that I use. As of a few days ago, most of the time when I click on a folder, choose Get Info, click on the icon, and choose Copy, nothing is copied. When I did this a few weeks back, it worked fine. (Confirmed with Show Clipboard in Finder). If I get an image into the clipboard, I can paste it into the Get Info window of a folder, it's just the copy that doesn't work.
And, in fact, sometimes the first time I do a copy after reboot it will work, but only sometimes.
I haven't changed permissions anywhere (and the problem affects all folders in my home folder tree). I recently did a Disk First Aid to confirm no errors on the disk. I did a Safe Boot, and it also didn't help.
Any thoughts?
Mac OS Big Sur 11.2.3. Intel.
Mac mini, macOS 10.13