Control system volume?

[Snapples]

I'd like to manually control my system volume. It seems to be linked to some other volume setting that I haven't figured out yet, but that's pretty useless.

Will a separate system volume slider be added?

Since it's not possible to root this phone (without making it halfway useless, anyway), it's not possible to replace the system sounds with quieter ones, so that's not an option.

[Keyakizaka46]

Yep very annoying, while the slider for media is muted, music with still come out in some apps, annoying especially you are in public spaces. Then what's the point of so-called 'system volume'? Shouldn't it override the app settings?