How can I make GC to stop automatically uploading activities.Prevent the app from connecting to the cloud-based Garmin Connect service.
I found nothing in the app settings itself and disabled background update in IOS settings.See https://forums.garmin.com/showthread.php?348180-Garmin-Connect-Mobile-Android-3-5-0-1-released&p=833857#post833857
If understood correctly from the thread you mention it is a bug.No, it means Garmin has decided that auto-upload remains enabled in Garmin Connect Mobile instead of being a user-selectable option, as of version 3.5 (which was a few minor versions ago). A design/policy decision, as opposed to an unintended fault in the programming (i.e. “bug”).
Switching Bluetooth of is currently no option,You misunderstood me. I meant disabling Internet access on your mobile device when you open the Garmin Connect Mobile app (which makes it pretty useless), and nothing to do with Bluetooth.
as I need the phone notifications.As far as I'm aware, the Garmin Connect Mobile does not need to be open on the mobile device for smartphone notifications to work on the watch. The app (as opposed to the device) certainly does not need to be connected to the cloud-based Garmin Connect service for the notifications to work.
You could also try turning off mobile data in the iOS settings and see if that is what you want. It will stop Garmin Connect Mobile talking to the Garmin servers altogether.