A possible answer is it’s not really a privacy setting but instead to save you from carrier data charges.

I agree that there should be an app firewall to the point I’m running an older phone w the checkm8 jailbreak to have a firewall.

On Android there is NetGuard which poses as a (local, running on the phone) VPN and allows you to deny / allow traffic based on process and domain. Works great, no root needed.

Then you can't run another VPN right? Then raw through Verizon with their tracking headers and stuff for anything non-https unless you go through the series of opt outs that get periodically invalidated with a new opt out needed.

Just checked, there doesn't seem to be an option for it (though technically it should be possible, I think). Sorry to hear about Verizon - hopefully mobile will soon be a viable option for you. Good luck!

You can run WireGuard (as a proxy not a VPN; ie, TCP/UDP only) with Rethink DNS + Firewall, an app I co-develop: https://github.com/celzero/rethink-app

On iOS it's also possible it's also possible to block Wi-fi data but only on iPhones sold in China: https://apple.stackexchange.com/a/312430

IIRC, there's separate permissions for web access and unrestricted internet access. The former is only apparent if you look for it on install, and isn't something you can disable on most ROMs.

I'm on OxygenOS 12 and I have the option to disable mobile data and/or Wi-Fi for each app, not sure if other versions have that though.