I have set SOUND_VOLUME 100, but alsamixer still shows 75 after a restart.
It looks like this might be an open issue: SOUND_VOLUME ignored on pi 3B+ · Issue #583 · balena-labs-projects/balena-sound · GitHub - what device type are you using?
I have a Pi 4.
It is also not the only setting that doesn’t get applied. I also set SOUND_DISABLE_SPOTIFY and the Spotify block is still running.