You can now unlock your iPhone using Face ID with a mask, and it works perfectly! This is a new feature in iPhone's latest iOS. Also, you can get iOS 15.4 early ...
Before you lock your iPad, you should set up a security method. Depending on your iPad model, this can include Touch ID or Face ID.
You can set up Face ID on an iPhone in just a few seconds in the "Face ID & Passcode" section of your phone's Settings app.