In the System menu, there are BGM, BGS, and SFX controls.
Yes, the game is made in RPGM. If you mean that to be feedback, you'll have to be more specific.
I wss blind as a bat about sound. Still, the the demonic showpiece has render problems. Also, flash/etc cutscenes are possible, regardless of RPGM.
You're playing on mobile? You can if you want, but it isn't officially supported.
Not everybody has a choice. Either fix it or don’t.