Just thought its worth posting with the impending release of FBSD 13.1 sometime soon (today), that updating with freebsd-update works fine with a iRedMail install. The upgrade does remove the /etc/ssl/certs/iRedMail.crt symlink (if you've setup certbot according to the docs) but fixing it and restarting postfix, dovecot, and nginx and all is well again.
Also updating all the installed ports to the latest releases also works fine (as of now, at least). Future note is php 7.4 is EOL coming this December, is there any plan to move to 8.0 or higher by then (or is it safe to update as-is anytime?)

Anyway, anyone on the fence on pulling the trigger on the update, go ahead, the water's fine!