Calendar appointments not showing up in Outlook app MacBook

Calendar invitations to a secondary outlook account (not default account) are only showing up in the browser version of the outlook account and now in the Outlook App version on my MacBook.

I have checked the outlook app is up to date - Version 16.98.

The Outlook app is attached to my default outlook account, and calendar invitations show in that account but not in the secondary outlook account I have set up in the Outlook app.

I can't find any useful checkboxes or even manual syncing in the Settings - which has been simplified by Apple to the point of being completely useless for situations like this.

An online search hasn't provided any useful advice either, as the settings instructions are all out of date and don't match the options offered in the current version of Settings.

I am at the point where I am going to have to call, which I don't want to do because I have found that these kinds of problems seem to be hard wired into the way Apple configures the devices now, taking more and more control away from users, and the folks on the end of the phone don't know how to fix it and have to come up with awkward work arounds. Now I'm complaining. But I would like to know if this is fixable.