Two basic troubleshooting steps to perform (test after each attempt):
A) 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).
B) If the issue persists, something could have gone wrong during the latest update procedure.
I would try to install a fresh copy of iOS (the latest available/supported by your device model, currently iOS 18.3.1). To do this, create a full backup of your iPhone (1), then restore it to factory settings (you need a computer to perform this step) and, in the end, set it up as new (2).
When done, restore data from your previously made backup (3).
Follow the instructions provided in these support articles:
(1) How to back up your iPhone, iPad, and iPod touch – Apple Support
(2) Restore your iPhone, iPad, or iPod to factory settings – Apple Support
(3) Restore your iPhone, iPad, or iPod touch from a backup
If the issue still persists, since your iPhone is covered by warranty, I suggest that you contact Apple Support directly, using this link:--> Contact Apple for support and service , or 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:
