Since I posted this topic I’ve had a couple of cases where all of the things that worked so far didn’t work. For those cases I found a different solution.
- In Finder, choose Go to Folder… from the Go menu.
- Copy and paste in this, then click Go:
/Applications/SketchUp 2021/SketchUp/Contents/MacOS/SketchUp
- Double-click on the SketchUp file.
That will run SketchUp as a Terminal process, and it doesn’t seem to be affected by the crashing issue.