Why is my iPhone 14 pro max discharging

If you already tried (to no avail) ALL the steps provided in the support article that led you here, since your iPhone is still covered by warranty, I suggest that you make an appointment (*) and have your device+charger+cable inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> https://locate.apple.com/choose-country-region . After checking it out, they'll give you all the available options.

Regards

Giulio

(*) You can do it:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above;
• Using the "Apple Store" app, available and downloadable from AppStore.