I'm experiencing the same thing on a 2018 iMac Pro. After entering my password to unlock my Mac, the screen freezes and my only option (after waiting over 5 minutes) is to power off and reboot. This has occurred multiple times since upgrading to Big Sur.
@arthurfromriga, I'm curious to know, are you using a Yubikey on your MacBook Pro? One hypothesis I have is that the issue is related to my Yubikey (which I use as a Smartcard and for two-factor authentication).
vready
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