Maybe this will help someone :
1. Go to https://connect.garmin.com/modern/calendar
2. Click the arrow on the top eight hand corner -> publish calander
3. Copy the link in the box
Open iPhone settings -> mail,contacts,calander -> add account -> other -> add subscribed calander -> paste link -> next -> save (no need for user and password) .
Thats it it was easier for me to have it on the iphone calander maybe this will help someone
Keep running ✌🏻️✌🏻✌🏻
Tamir