Android 9 set volume keys to adjust ringer by default
I was very frustrated when Android 9 changed the volume buttons to control the media volume all the time so I developed an app to fix this and make the volume buttons control the ringtone and notification volume as it used to. It's free and you can install it from here: [https://play.google.com/store/apps/details?id=com.softstackdev.volumeFix ]

Let me know if you need any help to use it.