My iphone 14 won't turn on

Perform a Forced Restart on the phone. Follow the instructions very carefully, as this is a bit tricky. You may need to repeat this several times.

Force restart iPhone - Apple Support

There are only 2 possible results when you perform a Forced Restart:

1) The phone returns to normal operation

or.....

2) There is a hardware problem with the phone that will need attention at the Apple Store (make an appointment) or take the phone to an authorized Apple Service shop.

You can find an authorized location in your area using this link: Find Locations

It's disappointing I understand. Did you try to force reset?

My iPhone 13 Pro Max 256GB Sierra Blue suddenly stopped working, and I tried all troubleshooting steps, but it remains unresponsive, now they want me to pay $900 for replacement.

Do fill out the feedback form, if there are many cases (I'm sure there are) they might do something about it. Feedback - iPhone - Apple