iOS 15.4's 'Use Face ID with a Mask' feature only works on iPhone 12 and newer devices
The recently launched iOS 15.4 update comes with a rather useful feature. It lets you unlock the phone with its Face ID when wearing a mask. According to Apple, it scans the "unique features around the eye area." But it looks like the feature requires more resources, as the company seems to be limiting its availability to newer iPhone and iPad models.