https://wccftech.com/ios-15-4-and-ipados-15-4-released-with-universal-control-promotion-support-for-third-party-apps-more/

Full and final version of iOS 15.4 and iPadOS 15.4 for iPhone and iPad is now available for download. You can grab the update over the air.

Compared to iOS 15.3 and iPadOS 15.3, the newly released iOS 15.4 and iPadOS 15.4 updates are packed with a ton of new features. This includes the ability to unlock your iPhone using Face ID while wearing a mask even if you are not wearing your Apple Watch, a handful of new emoji, 120Hz ProMotion support for third-party apps if you have an iPhone 13 Pro or Pro Max and, of course, Universal Control. The latter is a big one, given the feature was announced last year.