Since upgrading my iMAC (late 2017) from CATALINA to BIG SUR my system suddenly freezes and after a few minutes it crashes. I looks like it normally happens while in SLEEP MODE. That's the only hint, so far.
I have upgraded my MAC BOOK PRO (2018) without any problem.
iMac 27″, macOS 10.15
Uninstall all third party apps that are Cleaners/Optimizers/Anti-Virus
Kernel Panics are predominately caused by hardware faults or faulty third-party kernel extensions.
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Learn what to do if your computer restarts or shuts down unexpectedly, or you get a message that your computer restarted or shut down because of a problem.
If your Mac spontaneously restarts or displays a ... - Apple Support
https://support.apple.com/en-us/HT200553
Uninstall all third party apps that are Cleaners/Optimizers/Anti-Virus
Kernel Panics are predominately caused by hardware faults or faulty third-party kernel extensions.
—————————————————————————————————————
Learn what to do if your computer restarts or shuts down unexpectedly, or you get a message that your computer restarted or shut down because of a problem.
If your Mac spontaneously restarts or displays a ... - Apple Support
https://support.apple.com/en-us/HT200553
sudden long freeze then crash
