I was very late in updating to v1909, so my game only crashed last week. By digging pretty deep into the user forum at Steam, I found I wasn't alone, and there were a lot of suggestions that some person would say worked, only to find out that others couldn't reproduce it. This apparently went on for weeks, perhaps months.

Today I found a person who said that it was Windows Update v1909 that broke it, and that update v2004 fixed it. I tried it, and it worked. For me, anyway. It wasn't an Id software fix, it wasn't a Steam fix. It was a Microsoft fix.

tanstaafl.