Two basic troubleshooting steps to perform (test after each attempt):
A) In Settings>General>About check its iOS version and, if not already done, update it to the latest one (currently 18.3.1), using these instructions:--> Update your iPhone or iPad
B) If the issue persists, try a "forced" restart of your device using these instructions: Put it on charge for at least half an hour, then, keeping it plugged in, use these gestures:
In rapid sequence, press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the side (power) button. Only when the Apple logo appears (it might take 10-20 seconds), release that button (ignore all other screens that might appear, the one with the "slider" to turn the device off included).
If the issue still persists, since your device is covered by warranty, I suggest that you contact Apple Support directly, using this link:--> Contact Apple for support and service , or, even better, make an appointment (*) and have your device 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: