That option is at explore.garmin.com > Social > MapShare settings.
I haven't been able to find out what it is for. I have tried to mark a Waypoint with inReach and it is not shown in MapShare.
I only see that they can be shown if I add them to a collection that is shared on MapShare, but that also happens with any Activity, Track... etc. I don't see why there is a specific option for those Waypoint elements