Time is not set.
When choosing any region, the time is always California only. All solving problem tutorials do not work.
MacBook Air 13″, macOS 11.2
Depending on the nebulous tried everything definition, results may continue to vary.
• Set the date and time on your Mac - Apple Support
https://support.apple.com/guide/mac-help/set-the-date-and-time-mchlp2996/11.0/mac/11.0
You may need to study how to use Console &/or Terminal to get into underpinnings
of the issue; if you've actually tried everything else. Links within links can take you
to other places. Sometimes Calendar application setting has bearing on Time/Date.
A startup in Safe mode, is generally OK for troubleshooting issues; can resolve a few.
Second-user accounts are fair to try / see what is affected; if you have more than one.