iPhone 15 pro max Screen is blank

Try a Forced Restart by following these directions precisely:

• Press and quickly release the volume up button
• Then immediately press and quickly the volume down button
• Then immediate press and KEEP HOLDING the side power button and KEEP HOLDING it past the swipe to power off and KEEP HOLDING it until the screen goes dark and KEEP HOLDING it until you see the Apple Logo, then let go
• Sign back in with your passcode when prompted

I'm glad you got it up and running.