Yeah, since it's running stock Android, this is really a feature you'd have to ask Google for.
They *could*, but customisation is clearly not their plan for this range of phones, and for me that was the main selling point -- I *want* a stock Android phone, and since I don't rate the Motorola ones since Google sold them, I'm delighted I don't have to pay Pixel prices for that experience any more. As soon as OEMs start customising anything, you get slower security updates, and more bugs. Getting things implemented and fixed upstream is a much better model for everyone.
I tried Volume Control app, but it doesn´t work. When rise the notification volume, it rise the ringtone too.