Curiously enough, most apps talking to the network apparently don't even ask for firewall exemptions and just do it. The Windows-standard firewall exemption dialog window is suspiciously rare to be seen while almost everything today tries to contact network servers. This is why I installed Sphinx Software Windows 10 Firewall Control which apparently does a much better job detecting processes trying to reach the Internet (although it uses the same firewall engine built into Windows). I use it to block every app which doesn't really need the net to do the job I want it to do. Nevertheless it would be naïve to believe it gives 100% protection, there actually are plenty of ways to bypass a firewall.