If you've recently had your inbox migrated as part of our Microsoft 365 Migration, make note of whether your account shows up as Microsoft Exchange or Exchange/Office 365 Account. If your account still shows shows as Microsoft Exchange after a migration, removing and re-adding should force the account to switch over to Exchange/Office 365 Account.
(In this example we only use one account, but it's possible you may use multiple accounts.)
These steps will also be helpful if your mailbox has been moved from Microsoft Exchange to Microsoft 365 and your email account is not working correctly in Outlook on your Mac.
If you're suddenly unable to access your mail in Outlook on your Mac, or things aren't working quite as expected, you may want to try removing and re-adding your account to your mail app.