incedent detection unsuported

Well, when you choose Navigation, the watch has no idea on how you are going to move to your destination, and if that naturally involves sharp bumps and sudden stops which could trigger the incident detection. When you choose one of the supported activity types (https://www.garmin.com/en-US/legal/idtermsofuse/), then the watch can try to adjust the detection parameters so that it works for that type of activity (and even then, it will occasionally fail and either trigger needlessly or not trigger when it should).