Unable to add M365 shared mailbox to Mail

Anyone know what’s the latest with this?

my understanding is that since MS introduced security defaults to 365, older protocols have been blocked including IMAP which means that the old way of adding a shared mailbox in Mail no longer works.

I don’t want to turn off security defaults.

I know you can give the shared mailbox a password but this then enrols the mailbox for MFA :-(

The client doesn’t want to go to Outlook (although it’s free) and some of their Macs aren’t yet in MacOS 11.

So is there a solution that works???