I have checked these log files a few of times after installation and completely forgot them — thank you for the reminder, dear Nic!
Unfortunately, that FairEmail connection report does not contain a single error nor warning message. And indeed, FairEmail recognized and set up my Cyrus account without any warnings. This complaint came a bit later, when trying to synchronize email.
This is the full Cyrus report about connection with FairEmail — fair-cyrus.log
I have set up several different email accounts (Google, GMX, MS, Yahoo, Yandex, Vivaldi, Zoho) in FairEmail, all successfully. Vivaldi.net mail server seems to be based on Cyrus? Sorry, I don't have a FastMail account anymore — I wonder if that server talks to FairEmail.
