https://ioshacker.com/how-to/add-face-id-to-any-iphone-app
..if you want to add Face ID (or Touch ID) protection to any iPhone app of your choice, then there’s a workaround for that. This can be done with the help of the Shortcuts app and the Timer feature of the Clock app…
Using this workaround to add Face ID authentication has many benefits. For example, using this you can lock the whole Photos app instead of just protecting your hidden or recently deleted photos with Face ID.
Other apps you can protect with this method include messaging apps, Files app, Contacts, Mail, and any third-party app that contains sensitive information but does not feature support for Face ID protection…
