Face ID

If you still need help, reset Face ID, then set it up again. Go to Settings > Face ID & Passcode and tap Reset Face ID. Then tap Set up Face ID to set it up again. If you can't enroll your face, take your device to an Apple Retail Store or Apple Authorized Service Provider or contact Apple Support.

If Face ID isn't working on your iPhone or iPad Pro - Apple ...

Hi, update to ios 14.5. Did you try a hard reset?

quickly press and release the Volume Up button, then quickly press and release the Volume Down button. After that, press and hold the Side button on the right side of your phone. Keep pressing the button down (be sure to ignore the Power Off slider!) until the Apple logo appears, then release the Side button and wait for your iPhone to restart.

After that:

Go to Settings > Face ID & Passcode and tap Reset Face ID. Then tap Set up Face ID to set it up again. If you can't enroll your face, take your device to an Apple Retail Store or Apple Authorized Service Provider or contact Apple support.

HOPE THIS HELPS.