Can I use Face ID to lock the Messages app on iPhone?

You’re welcome …

… that said, your Lock Screen should STILL be your “Primary Shield” against unauthorized access.

And allowing “others” unsupervised access to your unlocked iPhone is still a really BAD idea.

Works great.

Just “Long Hold” the app icon and select from the dropdown.

If your FaceID malfunctions … it won’t work so well.

(Security safeguards are double-edged tools)