Disconnecting From Microsoft 365

Not sure what the issue is here when you mention both Microsoft 365 and Google Calendar.

I checked and I had connected Microsoft 365 when I tested it for a long time ago.

I verified that I saw my training in Office 365. Then I clicked the disconnect button.

After a few seconds I got a confirmation.

I then checked in Office 365 and all events from Connect were gone. Also no visible calendar for Connect in Office 365.

I sounds like you have shared the Connect calendar in Office 365 to your Google Calendar.

I connected with Office 365 again and tried that now by following this instruction: How to Share Office 365 Calendar With Google Calendar

That actually works great! I got 30 days of historic training into Google Calendar.

I've now removed the connection to Office 365 and Garmin Connect. The issue you have is that Google Calendar will still fetch events from the shared Connect calendar in Office 365, right? And that messes up Google Calendar in some way.

Why not just remove the shared calendar in Google Calendar?

The problem is that Garmin Connect calendars re-appear on my android phone every time I log-in my Microsoft 365 account using Google Email and Google Calendar. So on the left where you can choose which calendar you want visualize, I see the list of all the Garmin calendars that in the time I've sync with Google Connect feature. They don't disappear also if I've disconnected the account.. As the Garmin Connect features leaves some kind of 'footprint' that Microsoft 365 don't see, but Google Calendar see.

Online all is good, but on Apple devices and android devices, with Google Calendar App, the calendars still remain and there's no way to cancel them. 

But you know that online is impossible to log-in with a Microsoft 365 account. The problem is with the Google Calendar app

Google Calendar app both on iOS and Android let users log with Microsoft 365 accounts and that the problem... Garmin Calendars don't disappear, you can deselected them but You can't cancel them at allo, so every time you change device and re-connect Microsoft 365 account you'll see every Garmin Calendar you had connected in the time also if you disconnected them from your microsoft account on Garmin Connect

For Google Calendar you login with your Google account.
For Microsoft 365 you login with your Microsoft 365 account. They are not the same.

You might use the same email address and password for both but they are not the same.

To unsubscribe you go to the calendar settings, scroll down and click unsubscribe.

Your screenshot is from Microsoft 365, right?

But in any case, I repeat and explain, that you can also login in your Microsoft 365 account with Google Calendar and Google Mail app and your Microsoft 365 account, seeing your Microsoft 365 calendars with your Microsoft 365 account but on Google Calendar App! The problem is just in this specific case!

6713936 said:

Your screenshot is from Microsoft 365, right?

No, it is from Google Calendar. That is where you must remove the calendar. Garmin can't remove any Google Calendars that you've added. The only connection Garmin can do anything with is the one with Microsoft 365.