Hey Dinesh1718,
It appears that you're experiencing a problem with the screen of your iPhone 12. When you play certain games, part of the screen doesn't respond to touch. We're glad to glad to provide assistance.
Restart your iPhone - Apple Support -- The next time this happens, if you haven't already, see if restarting your iPhone helps.
If not, note the area that isn't responding and go back to the Home Screen. Does your iPhone respond to touch in the same area outside of the game? If it does, we recommend using the steps in this article to make sure it's not an issue with the app you're using: If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open - Apple Support
Let us know how that goes.
All the best.