Looking for an Android app that will allow me to use only the 3 apps I've explicitly whitelisted

[pepperminty]

I'm pepperminty and I'm a, gulp, phoneaholic. I've been sober for 23 minutes.

I'm looking for help. I'm looking for something that will lock down my phone and will only let me use one of three apps when I tell it to. The three apps are Amazon Kindle, Moon Reader, and Play Books.

I've checked out many other apps, but the problem with them, for my usage, is that they are "blacklist apps". They work by knowing what apps you want to block. For example, Facebook and Instagram. But I want to work on my netaholism the other way around. In other words. I want apps that I explicitly whitelist to be accessible to me. (The 3 reading apps I've specified).

Is there such an app?

I have a Samsung S9 running Android 8.0. Not rooted (and not rootable).

[mediclaser]

You could only do very little if your phone cannot be rooted. The closest you could get to what you want is to:
1) Disable all apps that your phone will allow you to (Settings)
2) Install NetGuard to control which apps you allow access to internet

[absque fenestris]

Possibly remove the SIM card...?
Lithium e.g. works quite well offline