My 14 pro max doesn’t support fast charging

If you have either dropped the device accidentally or exposed it to liquid or used it beyond acceptable temperature limits then…

Take your device to an Apple Retail Store or Apple Authorized Service Provider, or contact Apple Support:

Find Locations - Location Selector - Apple

Contact Apple for support and service - Apple Support 

Get a Genius Bar Reservation and Apple Support Options - Apple

Contact Genius Bar.

Manage Reservations - My Reservations - Apple

Take your phone in to be examined; it's obviously not operating properly for some reason and obviously is still under warranty.

Genius Bar Reservation and Apple Support Options - Apple

Yes, but note Apple may not be willing to provide warranty service outside Singapore depending upon the issue.

However they will happily check your phone for proper operation.

"Most Apple hardware comes with a one-year limited warranty and up to 90 days of complimentary technical support."

AppleCare Products - Apple (SG)