How do I choose which calendars to sync with Garmin watch?

Hello All,

My Garmin watch has a feature that shows the events of the day.  But it always shows no events.  I would like it to show my calendar events.  Do you know how I can do this?  I suspect that it might be expecting me to use apple's calendar app rather than using iCal standards that would support the use of any calendar.

Details:

- On my phone, Garmin Connect has: Settings > Phone Permissions > Calendar set to "Full Access" but has no way of specifying which calendar to get events from.

- My GarminConnect is installed on iOS

- My watch is a Vivoactive 5

- My most important calendar is on Fastmail, so has a standard iCal API.  For one company I also use their corporate google calendar so syncing that as well would be useful but most of my events are on Fastmail.  I do not use Apple calendar.  I deleted it.  Good riddance.

I found instructions for how to sync Google Calendar (static.garmincdn.com/.../sync_google.html), however Settings>Sync doesn't exist on my Garmin Connect. Maybe it has moved.  Also, it seems to be specific for Google Calendar, not generic for any calendar.

Any help would be appreciated.