I have reset my PRAM, unplugged and drained the capacitors, I have chosen pictures from new folders and from the same group the Catalina Dynamic desktop is from... nothing sticks. FWIW the desktop on my second monitor stays on the chosen pict. I have booted into Diagnostics and it passed. I have run TechTool 13 and everything passes. I am a believer in beating on things until the options run out. This post is one such option. I would appreciate some ideas.