Recently, I reported that Safari was crashing in the most recent Big Sur Developer Beta. I did a little more research and discovered (at least in my case) the problem was Extensions in Safari. When I turned off all Extensions, the Safari crashing problem was gone. I did re-activate a few Extensions with no issues. I narrowed the problem down to the MarsEdit blog App Extension which was causing the problem. If you are testing Big Sur and having Safari crashing issues, try deactivating all your Extensions.