Thanks for your reply. Best thing is just to test it with a new clean install of resbian I guess.
I also found this post but after I posted my own question.
I find the possibility of using an app to “shut down” the system also great and hope this also works for an Android device.
I’ll just have to use my breadboard and test it out. But I think I’ll order a Pi zero W for that purpose.
If I screw it up it only costed about €10,-