Outlook will not open at all and the only message I get is the one in my original question.
I checked my pst file and I have full access.
Instead of just resetting the permissions for your pst-file, reset the permissions for your entire user folder. This process is explained in the entire article that "Melon Chen CHN" copied the previous instructions from;
PST File access is denied after upgrading to Windows 10
Note that when you switched from a local account to a Microsoft Account, you select the Microsoft Account and not your local account for the permissions. You can of course also add both.