Using older versions of Outlook for Mac for personal email and calendar
I was having this same problem this morning! Max crashed and corrupted a bunch of MS related profiles I think.
I went into the Account settings and removed the problematic account, signed back in and it seems to have resolved the issue.
I noticed when it was happening on my account that it was mostly "cloud/online" emails that had the issue, anything recently received or sent and stored locally on my device didn't have the same issue.
I was also getting stuck in a loading loop trying to reply to emails stored on the cloud.
Hopefully this is helpful to someone!