Hi everyone. I just decided to share with you my experience. After installing Norton Security with macOS Big Sur 11.4, my MPB16" 2019 started to behave like described. I'll add some detail. I had two accounts, normal user and admin user. Both of them could not connect to wifi network, and after a few minutes of work with both of them my computer's fans sped up noisy, black screen, computer rebooted and showed "your computer has rebooted because of a problem" screen (black screen, not the pop up already in logged os). I tried to reinstall the os plenty of times maintaining my hard drive partitions scheme. At some point before the completion of the process, same issue, fan sped up abruptly and all went to reboot because of a problem. However this problem did not occur at all with safe mode, which could connect to wifi normally and did not crash, though it was really slow and heaty. I tried as well to update to Big Sur 11.5 from safe mode, no luck at all, because it reboots to complete and then the problem starts again blocking any progress. The only solution for me was to delete the partition table. After reformatting the chosen drive for Macos, I could go into macosX base system and reinstall Big Sur onto it. So now I'm using it without any problem, it upgraded straight to 11.5 automatically. I believe something (Norton? not sure) put in the hard drive some file acting like a trojan, some persistent "venom" which was being constantly parsed even during os reinstall process. I don't know where it came from, not sure if this is an explanation. Deleting partition table "removed" it, so the clean install process could go over that sector which before was the place where this file, being parsed, caused the stop. Since the entire machine was under pressure even if idle, I believe this file was a service being run. The fact that safe mode run without any problem should confirm it. Unfortunately I was not able to map it and see what was it, because system monitor, when run, did not display anything, as it was being forbidden to access pids list. So, while it's not a full solution, if you are dealing with this situation, deleting the old partition and making a clean reinstall solved everything for me. Hope it helps.