But I have a question, somehow I have a little performance overview on my game screen, that is in no other app. Is it from the game itself? And if so, how can I remove it? I play v0.17.0 on Android.
No, it's not from CK - there would be no point in having a performance overview on a 2D visual novel (it'll run at 60fps on a potato). It will be from another app you have installed. My guess would be Nvidia, as they love their weird little overlays.