[Daho0n]

What you are looking at is like buying an iPhone and wanting to block Apple. You won't be able to from the phone itself (unless you flash another ROM but then you'd be better off buying something like a pine phone).

If you are really serious and you won't flash a new ROM then you will need to filter the traffic after it leaves the phone as you cannot trust the phone or its apps. IMO the only way to do this is to use a VPN to connect to a device that runs a proper firewall. It could either be a Raspberry Pi you carry around (bit too geeky for me) or a server somewhere you trust. I connect to a pfsense machine at home via VPN and filter traffic with pfblockerng. You can block on geography if you want.

My girlfriend's iPhone is just as bad as my OnePlus..