The same thing happened to me a few months ago. The power button went first, and then the bottom volume button some weeks later. I changed my phone battery today and discovered the little plastic bits had basically degraded and crumbled. So now even though my phone is charged up, I can’t get it to turn on and I haven’t seen anything on any forums about what to do about this specific problem. You posted this since 2019, have you had any luck since then? Buying a new phone is not an option for me.