Iphonenxsmax

If you're using a screen protector and/or a case, try to remove them.

Try also a forced restart of your device:--> Force restart iPhone - Apple Support

If the issue still persists, since your device is stll covered by warranty, have it inspected at an Apple Store or AASP:

Apple – Location Selector

Regards

Giulio

If you are having problems with your touch screen, you need to get an appointment at an Apple Store for an evaluation.