First spotted by Brandon Butch, iOS 15.4 will offer support for Face ID while wearing a mask. The text on the setup screen implies that it focuses more on the area around a user’s eyes to make a match. As Federico Viticci documented, it allows you to add pairs of glasses too, which makes sense for greater sensitivity around that specific area.
For what it is worth, I just set it up and it works perfectly. It may have been a long time coming for those of us who do not wear an Apple Watch, but I am glad to have this now.