Hey Rejesh - the camera is going to use the most power and in turn you might experience a tempature increase vs. normal operating tempature. Phones typically operate up to 45℃. I’d suggest looking at:
What apps are using the most battery? Are any apps using considerable background processing power?
Does a reset of the device fix the temperature issues you’re experiencing?
If you’re truly concerned still I’d contact Nothing support or give the feedback in settings > system > feedback.
also, if you phone is new it might be that it is still learning your habits which might result in a higher than normal tempature.