Face ID with Mask on iPhone 11 models and older
Apple haven't released Face ID with Mask on iPhone 11 models and older. Idk why they did this. But iPhone 11 owners too want to have that feature.
The Camera hardware on iPhones 11 and older do to support this feature.
The Cameras on iPhone 12 and later do.
Don't expect to see that feature on older phones. It's simply not possible to magically make them work like newer phones with newer hardware.