Mail immediately crashes on openig

Press and hold a Shift key while launching Mail from Applications or the Dock. That action causes the Mail app to open with no message selected.

Release the Shift key when and if the Mail message viewer window opens and remains open.

In so doing you might be able to isolate the problem to a malformed message causing Mail to crash. If you are fortunate enough to find the problematic message, the ideal solution is to use the email account's webmail interface to delete it.

If Mail remains open long enough to not crash, you might try rebuilding Mailboxes according to Rebuild mailboxes in Mail on Mac - Apple Support. You can rebuild any Mailbox including Junk, Trash, Outbox, Sent, etc. You might as well rebuild all of them.

If nothing helps "Safe Mode" may be instructive: How to use safe mode on your Mac - Apple Support.

For reference: If you can’t send or receive email on your Mac - Apple Support

👍

That would have been the last step, which is a good thing because after that I'd be out of ideas.