Put it on charge for at least half an hour, then, keeping it plugged in, try a "forced" restart of your 14, using these instructions:
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 persists, 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: