Hide music from list of alarm, notifications, and ring tone files
I had the same problem on my OnePlus 7. It's irritating that the Oxygen OS pick menu doesn't have a  search () option.
To over come this I use Ring Tone Maker. You search for a tone, long press and from 3 dots menu on right, choose to set it as a ring/alarm/notification tone. Drawback of this approach is that you can't find default tones in this app. If your device is rooted, you could locate those files and copy in some folder that would show up on this app