There is a large thread on this in the Catalina forums. At least for this specific crash, it can be traced back to a bug in "mediaanalysisd" - there certainly may be other reasons why the computer is crashing on idle, but this is clearly ONE possibility. Usually after every upgrade of OS, or any point release that updates the photos app, I need to run with a single monitor for several days before the crashes are eliminated. Silly, I know. I have tried to create a support ticket on this with Apple multiple times, but all I ever get is "send in your computer for replacement"