This Volume App for Mac Lets You Do More With Your Earbuds and Speakers

SoundSource 6 for Mac adds support for AirPlay speakers and lets you set a per-app EQ. It allows you to control volume levels ...
Techno-Science.net

How to Use Separate App Sound on Samsung Phones to Control Audio Output for Different Apps

To use Separate App Sound on a Samsung Galaxy phone, go to Settings > Sounds and Vibration > Separate App Sound, toggle it on, choose the app (e.g., Spotify), and select the audio device (e.g., ...