users can activate the built-in app lock feature in M31, M21 device using Activity launcher app which is available in play store.
Download the Activity launcher, open it, seach app lock in it, click on it to activate it.
Link to activity launcher: https://play.google.com/store/apps/details?id=de.szalkowski.activitylauncher
i can't see paint app. is the name of the app in activity launcher something different ?
