So, I was having this really frustrating issue with my iMac Retina 5K 4 GHz Quad-Core Intel Core i7 after I upgraded to Big Sur, it would crash randomly about 10 times a day. After days and days researching without success I finally stumbled upon a list of easy fixes you can try, including resetting your Mac's NVRAM, which I did. It's been 3 days and no crashes yet. Some of you might have done this already, but for those of you who haven't, this might be the solution you were looking for. The list of easy fixes was posted by Michael ****** in his website and it's called "The Top 11 Tricks to Fix Common Mac Problems Quickly". I might add that along with this I also cleared all the caches and deleted some apps I even forgot I had. Hope this helps someone.