I did exactly the same thing using NetGuard. It opens your eyes to how much tracking happens with almost every app.

I also block Wi-Fi and mobile data access wholesale for apps like virtual keyboards and most pre-loaded crapware that can't be uninstalled.

Ive been meaning to make a PR of feature request to add individual URLs to the blocklist

I found NoRoot Firewall to be a much more powerful app. It allows you to add global domain filters too. And for some reason the logging of apps which request internet access appears to be much more detailed.

How do you do that?