Apple has released iOS 15.4, an update that brings improved Face ID support and the ability to store EU Digital COVID certificates without needing a dedicated app. iOS 15.4 is available to the iPhone 6s or newer, but Apple restricts some enhancements and features to the iPhone 12 and iPhone 13 series.
https://www.notebookcheck.net/iOS-15-4-begins-rolling-out-to-the-iPhone-6s-or-newer-with-Face-ID-improvements-for-the-iPhone-12-and-iPhone-13-series.608337.0.html