Lock the minimum and maximum audio volumes on your device. You can lock each type of audio volume separately. It helps prevent accidental or unwanted volume changes. The full version can run on start up (optional), has a password option, has a home screen widget, and has a dark/light/black/amber theme option.

Full Version Link
https://play.google.com/store/apps/details?id=com.grantojanen.audioCrankClamp

More Details
Offline: Yes
Lightweight: less than 1MB
Multi-Window Support: Yes
Descriptor: audio volume locker

Permissions Info
Foreground Services: This is needed to run the volume lock service on Android 9+.
modify Do Not Disturb settings: This is needed to set a minimum volume lock on the ringer, notifications, and alarms on Android 6+.