Apple Mail keeps crashing on launch

Press and hold a Shift key while launching Mail from Applications or the Dock. Release the Shift key when Mail opens.

That action causes the Mail app to open with no message selected.

Yes. Open  (Apple menu) > System Preferences... > Internet Accounts and remove the problematic email account. Then, add that email account again. Those steps are described in Add or remove email accounts in Mail on Mac - Apple Support. Follow them in reverse order—in other words first remove, and then add that same account.

If you have more than one email service provider, remove them one at a time. Launch Mail after each account removal, to determine if you removed an affected account.

It opens the mail program with no choices. But, when I click on all messages, it quits immediately. What's next?

Just curious why this is necessary? Is it an MFA thing, or just an update to an old OS?

John -

I'm having the same problem and the SHIFT key trick helps. However, there is some issue with one of my mailboxes that seems to be creating the crash. As long as I don't select the 4QS mailbox my Mail app works fine. When I select my 4QS account Mail crashes. This is an IMAP account that I've deleted and recreated multiple times. It seemed to work for a couple of weeks but now it's crashing again and I've had no luck with recreating it. I've also logged in to the webmail account and removed everything but a few needed messages.

Any other ideas?