Just install AFWall+ or NetGuard from F-Droid and set that only whitelisted apps allowed to connect. I don't see a need to create separate mod for this.

I haven't used these, but the problem here being that the user who can set up a whitelist will (presumably) be just as easily able to edit the whitelist.

Along with that I've had issues in the past with whitelists where I disabled something where the IP address wound up being a dependency for something else I was using.

You whitelist apps in those firewalls, not IPs. But I think I saw there some IP lists also.

The easy way is just to turn off both Wi-Fi and mobile data, either by using specific toggles or by switching to airplane mode.

Note that in airplane mode, it will shut off Wi-Fi, but you can turn it back on.

Nah man, you're misunderstanding. I mean a phone in which the OS does not give the user the option to access stuff. This is a self-restraint thing and there's a (small) market right now for phones that can only do basic functionality (i.e. message, call, address book and maybe an alarm), it seems to me that it _should_ be possible to permanently disable wifi on an Android ROM, and potentially (although probably much less likely) make data almost impossible to use.

It's far easier to not be tempted by something you have no immediate means of accessing than something that's a toggle away.

You can do it. I've built custom ROMs from the lineage code base that stripped out Bluetooth, GPS, phone, messaging, etc. It's not that hard, just time consuming.

Cool! Was there any reason you were doing it?

Almost certainly beyond my skill level but outta curiosity, is disabling data (meaning all uses of the network other than fundamental things like texts and calls) something that could be done? I suspect probably not

Could you not just disable wifi on any android phone? Turn it off and keep it off? I do this pretty regularly just to save battery life