Sigh. Do you have any experience with thing black lines appearing on the screen? Then if I move a finder folder or switch apps, the photos leave remains. I followed most of the instructions I found on Google, other than updating to the newest OS. I'm assuming I've got a connection issue?
MacBook Pro, 15 inche 2019 (old, I know) and I attached the rest of the "about this mac section." I'll get on my phone and try to attach a picture of my screen.