Apple has unveiled the first iOS 15.4 beta, following the public release of iOS 15.3. The inaugural iOS 15.4 beta brings a few new features to iPhones, such as third-party support for ProMotion displays, currently restricted to the iPhone 13 Pro and iPhone 13 Pro Max. Apple has added two COVID-related features, too.
https://www.notebookcheck.net/Apple-to-bring-120-Hz-upgrades-Face-ID-with-a-mask-and-vaccination-passes-to-iPhones-with-iOS-15-4.596328.0.html