I believe the problem is that outlook doesn't support caldav, or Android doesn't, or both don't. Anyway the solution is to add the outlook account as an exchange account manually.
If u have 2fa, you'll need to create an app password. Then follow the instructions at https://support.google.com/calendar/thread/79532447?hl=en&msgid=81434194
Now your personal outlook will sync over the exchange activesync (EAS) protocol which 1) has calendar info and 2) Android supports
Vivaldi is chromium