I wrote this later post, with what I had figured out after the first post:
One thing I learned was that if you had crashed with 2021.0, updating to 2021.0.1 in the normal way could leave you still with a crashing issue. For most people that was solved by deleting the existing SketchUp 2021 folder in Applications, before copying in the 2021.0.1 version.
Even that didn’t fix all cases. For some of those I am able to see whether SketchUp is being run normally by macOS, by looking at the crash logs. Have you sent in any bugsplats that I can check? I couldn’t find any with your email address, but if you can tell me a date and time you sent one in, or even easier, if you know your public IP address, I could track them down. Or, just make sure to include your email address in the next one that you send in.
Depending on what I can see in the crash log, I may have another suggestion of something for you to try.
If you look at a Time Machine entry that is earlier than January 17th, and it says SketchUp is 2021.0.392, that’s an oddity with Time Machine. Before that date it should show as 2021.0.338.