I´ve had the same issues that this thread has for a couple of months now, and have tapped AppleCare several times; their recommendations match those steps several have taken in the below discussion.
On my (high-spec) iMac Pro 2017 I believe I have isolated the source of the problem: my two external Dell 5k monitors (Thunderbolt/USB-C). That tallies up well with other forum comments elsewhere.
The issue arose post Catalina and has continued with Big Sur (currently Big Sur 11.1).
The kernel panic crash happens either when I put the iMac to sleep without first turning off the two external monitors. Furthermore, the whole OS freezes (cursor and all) occasionally when stepping away from the computer - completely unresponsive.
These issues do not occur when the two external monitors are turned off.
Apple - please review and correct your OS...
Lars_T_1
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