I have the same question. I tried the "new" Outlook when it appeared as an option. Looked interesting but I switched back to Outlook 365 almost immediately as I assumed it would not work with Go Contact.
I have had what appears to be exactly the same issue for some time - the error messages are now daily and their frequency is increasing. It is becoming more than just an annoyance as I cannot be certain that synchronization has been successful. Win 10 Pro 21H1 19043.1266 Outlook 365 CalDAv 4.1.0