Random photos in a desktop folder appear as white icons

There may be something amiss with some of the files. How did these files come to your Mac? Do you use iCloud Photos or iCloud Drive? Do you use "Optimize Storage?"

What happens if you open one of these pictures in Preview? How about it you export it back? What do you see with these (and the other) files when they are imported to Photos?

Have you  tried these steps:

• Rstart Finder (Apple>Force Quit>Finder?)
• 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 

• 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. 

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…