Sorry for the long delay, but I haven't played Minecraft in years I wrote these plugins a few years ago as a past-time to put on my server and uploaded them here in case anyone else might find them useful. I might get back into it since there's been quite a few changes since I last played.
Anyway, I just tested PaintingProtect on my server and it works fine. Other players can't break paintings that I place, and I can't break other players' painting unless I'm holding my Op Stick. It's working perfectly as far as I can tell.
I do plan to recompile all my plugins for 1.18 over the next few weeks, so maybe try it when I upload a new version...