Using Face ID while wearing a mask requires relatively recent hardware. Consult this list of iPhone models that support Face ID with a mask to see if yours is compatible.
Which iPhones support unlocking with Face ID while wearing a mask?
iPadOS 15.4
iOS 15.4 is now available with easier Face ID unlocking, Universal Control and more
Apple has released iOS 15.4 for the iPhone and iPod touch, as well as iPadOS 15.4 for iPads, bringing new features such as unlocking your iPhone with a mask on.
iOS 15.4 release in the first half of March, iOS 16 development moving fairly smoothly
Apple should release iOS 15.4 in the first half of March following new hardware unveilings as development work on iOS 16, the next major update to the iPhone operating system, continues unabated, according to a reliable source.
iOS 15.4 lets more people download iOS software updates via 4G LTE cellular data
Apple's iOS 15.4 lets some users in previously unsupported locations download over-the-air iPhone software updates via 4G LTE cellular networks.
Second public betas of iOS 15.4, macOS Monterey 12.3 and tvOS 15.4 have arrived
Apple has launched a second iOS 15 public beta, as well as released second betas of iOS 15.4, iPadOS 15.4, macOS Monterey 12.3 and tvOS 15.4 to public beta testers.
How to run Shortcuts automations without the pesky notification banner
Learn how to execute personal iOS automations in the Shortcuts app on your iPhone and iPad completely silently, without ever seeing the annoying notification banner.
iOS 15.4 lets iPhone apps offer ProMotion 120Hz refresh rates for all animations
Apple with iOS 15.4 has reportedly fixed a Core Animation bug that has resulted in a sub-par ProMotion experience. Now all third-party apps automatically use smooth 120Hz animations on iPhones that feature support for ProMotion display technology.
iOS 15.4 beta includes support for receiving notifications from web apps on iPhone and iPad
Apple's iOS 15.4 and iPadOS 15.4 updates, currently in beta, apparently feature support for receiving web notifications in the Notification Center on your iPhone and iPad.
You need to have an iPhone 12 or newer to use Face ID with a mask
A new feature in iOS 15.4 and iPadOS 15.4 for using Face ID while wearing a mask requires at least the iPhone 12: it won't work on the iPhone 11 and the iPhone X or older.