The upcoming iOS 16 update will finally enable always-on display (AOD) functionality, according to Bloomberg's Mark Gurman. However, the AOD feature will only make it to the iPhone 14 Pro and iPhone 14 Pro Max as they are touted to sport LTPO displays that can potentially refresh as low as once per minute similar to the newer Apple Watch models.
https://www.notebookcheck.net/iOS-16-will-enable-always-on-display-but-only-on-the-iPhone-14-Pro-and-iPhone-14-Pro-Max.623140.0.html