While it’s true that iOS 15.4 is a minor software update for iOS, it’s rather important as it finally allows Face ID to unlock your iPhone when you’re wearing your face mask on. This doesn’t require you to have an Apple Watch on you, but you will need an iPhone 12 or higher to make use of the feature. That’s because your iPhone has to scan a much smaller area to authenticate it’s you, which is a more intensive process, so Apple has limited it to newer iPhones and iPads only. To make use of the improved Face ID features, you’ll need an iPhone 12 or newer.