Unfortunately this doesn't work for notifications such as 'lap times' from the Garmin app. This is also considered media by the phone.
Adding per app volume control is IMHO a really bad UX. It means there's a master volume and then per app volume is like a coefficient the app volume is multiplied by.
My car has its own volume control separate from the phone bluetooth volume and I hate the experience of having two volume knobs interacting with each other when all I want to do is to increase or decrese volume
I really prefer it for having different things set at different volumes. Like presets.