macOS Big Sur YubiKey Login Freezing Issue
After upgrading to macOS Big Sur's update on 11/19/20, the login screen freezes intermittently, after entering the YubiKey login pin, requiring the MacBook Pro to be shut down completely and turned on again.
The YubiKey issue has been documented from a few sources.

Reddit - MacOS Big Sur SmartCard Authentication issues
Apple Discussions

Stuck at lock screen, macOS Big Sur
Big Sur and smart cards



MacBook Pro Configuration

Two-Factor authentication enabled with a YubiKey 5C
OS: macOS Big Sur, Version 11.0.1
Device: MacBook Pro (15-inch, 2019)
Processor: 2.3 GHz 8-Core Intel Core i9
Memory: 32 GB 2400 MHz DDR4

Attempted Solutions

Restart the computer.
Shutdown and turn back on.
Reset NVRAM. See: Reset NVRAM or PRAM on your Mac
Reset SMC. See: How to reset the SMC of your Mac
Run Disk Utility's First Aid: No issues found
Run Apple Diagnostics: No issues found
Scan computer with AVG Antivirus: No viruses found
Reinstall Big Sur from macOS Recovery
Remove apps from starting automatically at login. Specifically, there was a Zoom app that I removed from starting at login. See: Add or remove automatic items
Run in safe mode: The frozen login screen still persists intermittently in safe mode. See: How to use safe mode on your Mac
Performing a factory reset and restoring the system from a Time Machine backup has resolved the login freezing issue with Yubikey's Yubico 5C.
The Time Machine backup restored to the Mac was created right before doing the factory reset.