A metered lte location would benefit from most restricted data possible. Question is how to basically stop all traffic except a few? Currently I have adguard on with a number of sites and about as large of a hosts file as I can without breaking it.
Suggestions online are DNS port and Pi-hole or allow specific IP and block rest.
The ! is a special operator, meaning except, or false, but it cannot be applied on every field, it does also work on mac source addresses and dest addresses.