Original problem is trying to activate SketchUp Pro 2021 using the activation_info.txt file but I had already started SketchUp Pro.
I found an article on this form (2016 activation_info.txt not working) regarding this for 2016 version and I wanted to try for 2021 version, but it didn’t work, so I thought I might try to uninstall it and reinstall it and do this before starting the program.