There are few ways to turn on a phone with a broken power button, unless you're willing to work to get your hands dirty with developer settings.

To turn on an Android phone without Power button, put the phone in fastbooot mode using Volume Up+Volume Down and connect the phone to a computer. Download and install the universal ADB drivers on ...

Google Pixel and Samsung phones have taken over power menus by forcing Assistant and Bixby on you. You can change them back to power menus.