I don't know why it is so difficult to provide a simple in-built app lock like every other oem is providing in their skins. Secure folder is great but it's not an app locker,
If you want to have two instances of an app and lock them both, you can't do that using secure folder, at most you can only lock one app and the one you have out of the secure folder will stay unlocked, unless you use an external app locker.
If you don't want to have an app in secure folder because you want it running in your main storage, like where you can access everything you have out of secure folder but just want to lock the app, it's not possible again.
If you try to get external app locker, firstly they are not good, not reliable, sluggish and have tons of ads, and they don't even detect the instances of the app you make using dual messenger.
People have been asking for an inbuilt App Lock in OneUI for quite a while now, but looks like Samsung is just busy doing the extraordinary while missing out on the basics. Good work, Apple!
