hi im having the same problem as well but im quite sure its not apps because i hadnt installed anything before it happened and im fairly certain its because it got a bit wet this week.
i was washing my puppy on a videocall when i realized the place i was resting the phone had water on it, and i was placing the charging plug and speakers down no less. so im fairly certain it got wet. so i immediately turn off the phone after realizing where it was. i didnt put the phone on rice since only its butt was wet. so it remained turned off while i let the butt side dry by facing the butt side towards a fan. i did that at night and the next morning i turned the phone on again and works fine.
after a while tho the volume thing happened and is still happening as im typing this. at times, the side buttons (power button, volume up and down) wouldnt work and i d have to wait till it automatically shuts its screen down to close it. the volume would shoot up but i noticed it happens more likely when its hooked to a charger, when i can feel a bir more heat.
what do i do? hope someone gets to read this and helps me
how do i fix it? do i just let the phone