The concept of having an Apps’ volume and a system volume was one of the first that Android removed.
Thus, many people find it strange.
For viewing movies I found Celluloid (Flatpak) to be the best of all. Haruna could surpass it, if some basic issues are dealt with.
How could the app change the system volume, i.e. mirror the system volume on it’s volume slider?
Would this need a code change, or could some trick work here?
Celluloid uses Pipewire natively and works without device access or Pulseaudio permission.