OnePlus
Lock Apps with an Extra Password auf OnePlus
App locker is the OxygenOS feature responsible for asking a second time for your unlock method before specific apps open, even while the phone itself is already unlocked. It reuses your existing lock screen password or pattern, so there is no separate code to remember.
To set it up, go to Open the Settings ➔ Tap on Utilities ➔ Tap on App locker ➔ Tap on Add apps ➔ Choose the desired apps ➔ Tap on Back. Every app added here now asks for the lock screen credential before it opens, regardless of who unlocked the phone.
Back on the App locker screen, you can also toggle Enable or disable Hide notification content. Turning it on replaces message previews from locked apps with a generic notice on the lock screen and in the notification shade, so titles and message text stay hidden until you unlock the app itself.
App locker only adds a second prompt for the apps you choose. It does not replace a missing lock screen password, so set one up first if your phone is not protected at all. It also has no effect on apps opened through widgets that bypass the app icon, since those can show limited content without triggering the lock.