Why is my face is disabled

This is what you need to do. If your Face ID is not working, see this, If Face ID isn't working on your iPhone or iPad Pro - Apple Support and this If an alert says Face ID has been disabled on your iPhone or iPad Pro - Apple Support. If neither help, then use the Get Support link at the top of the page here to contact Apple Support for service.

Have you had the screen replaced? Sometimes replacing the screen disables Face ID on the newer models.

Note: This only happens when your screen is replaced by Non-Apple certified repairers.

PS: I found an Apple Support article relating to this, it might help: https://support.apple.com/en-us/HT208186