This is a super common issue following back glass replacement on most iPhone models.There is typically a small gap in the chassis where the flex cables lives. It's all too easy to accidentally nick it when removing the old back glass. The little arm of the [link|https://www.mobilesentrix.com/power-button-flex-cable-for-iphone-12-pro-max|cable that handles the power button|new_window=true] is extremely narrow. So it doesn't take much.