I had a working connection between Garmin and Office 365 - until 12 days ago.
Since then apparently the link between Garmin and O365 is broken.
Does not show up in the Account Information (Applications: You’ve given the following applications permission to interact with your Garmin Connect account.)
Clicking on the 3 dots and then "connect to Office 365 calendar" then prompts for O365 credentials - then nothing, switches back to calendar, but no sync established.
In the Android Garmin Connect App
Settings | Partner-Apps | Microsoft Office 365 = can enter credentials =error message
So, not working.