The answer @kyriaqos has provided saved me and solved my issue. Resetting the SMC is the solution!!! I upgraded from Catalina to Big Sur 11.1 and could log into my account but could not unlock my system preferences. Let's just say there was a bit of panic involved. Not sure how this fits the philosophy of "it just works" but glad someone worked it out! Thanks @kyriaqos.
blauerplums
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