Apple has suggested the existence of a 120Hz display on the iPhone 12 series through iOS 14 beta 5. The latest iOS beta version carries an option that lets iPhone 11 Pro users limit the frame rate to 60Hz.

source https://gadgets.ndtv.com/mobiles/news/iphone-12-pro-max-120hz-promotion-display-refresh-rate-ios-14-beta-5-apple-2284333#rss-gadgets-all