Mail can't verify the identity of the server outlook.office365.com (Passwordless account)
I have a Microsoft Exchange email account set up in mail (Catalina 10.15.7) on Mac. I've switched to passwordless access & use Microsoft's password app generator to produce a password for verification. Everything works fine for about a week then I get the above warning & cannot download any emails. If I delete the account, reinstall & generate a new password mail will work fine again for another week.
I've tried to trust the certificate but there is no "Show certificate" button in the warning box. I've been through key chain but can't find the certificate. Outlook works fine on my iPhone.
If anyone can point me in the right direction as I've search everywhere for an answer and can't find anything. Deleting the account & reinstalling weekly is a pain.
iMac 27″, macOS 10.15