I had the same issue after upgrading to Big Sur. Computer would crash every five minutes with no applications running (just sitting idle). Apple walked me through the following steps. Boot into Safe Mode and see if computer crashes (it did eventually) Create a new user account and see if the computer crashes (it did) These didn't solve my problem, but may be helpful for others. Eventually, I needed to boot into Internet Recover mode (Shift-Command-R), erase hard drive, reformat hard drive, and re-install Big Sur. Once I did that, the problem was resolved. A radical solution, but it worked. Apple was very helpful in resolving this problem. On the positive side, a new install was a nice refresh and my laptop runs faster. Luckily, I had all my data files in my Apple iCloud Drive.