I had the same problem and managed to fix it - over at apple.stackexchange is a great thread and a description how I fixed it https://apple.stackexchange.com/a/468997/102293

To me it happened from one moment to the other. My Mac has forgotten all timezones i.e. "sudo systemsetup listtimezones" returns an empty list, the default timezone is GMT and my mac thinks I am in Cupertino,CA. Timezone in Preferences shows as "Unknown". I wouldn't care but it's messing up all my Outlook appointments as well as single-sign-ons (e.g. can't login to web ms teams anymore).