it is not that smart notifications - it is the link/sync feature of how the phone and watch are linked via bluetooth.
I believe the fix - is to disable Bluetooth on the phone (or maybe just watch?) - only activating it when you want to allow the sync feature (update Garmin account with steps/HR, update weather, calendar, etc)
However that disables a good portion of the Watches features....so kind of screwed either way. I'm living with the phone drain.... praying for an update.... :-/
My fix was to remove the location permission for GC in my phone settings.Ah. No wonder I never (to my recollection) experienced undue battery drain even though Garmin Connect Mobile is running on my Android handset, because I tend to only enable Location service when required for navigation (and disable it again afterwards), and also make a habit of removing specific permissions from apps when I don't see how it contributes to my use cases.
This breaks the Garmin weather widget but I am sure there are third party weather widgets that should help.