Hello AppleSiggy,
We see that you're having an issue with Face ID on your iPhone 12 Pro Max. What you're experiencing is not expected behavior, and we'd be happy to look into this with you.
First, restart your iPhone and then test to see if the issue remains.
Restart your iPhone
If the issue persists, reset Face ID. Go to Settings > Face ID & Passcode and tap Reset Face ID. Then set up Face ID again and test to see if the issue remains.
Use Face ID on your iPhone or iPad Pro
Let us know how's this goes.
Have a great day!