Open the Samsung app you want to lock
Tap the Recent apps button
Tap the app icon at the top of the app card
Select Lock this app
If Lock this app is not available, use Secure Folder
Open Settings
Tap Security and privacy
Tap Secure Folder
Sign in with your Samsung account
Set up a lock type
Open Secure Folder
Tap Add apps
Select the apps you want to protect
Tap Add
Keep Secure Folder locked when not in use