GlassWire does not touch the Windows Firewall API until you switch our Firewall to “On”. We do this because many IT/Infosec professionals sometimes set up their own rules and they don’t want the firewall rules touched. They use GlassWire is a visibility tool instead of a firewall in some cases.
If you switch GlassWire to “On” we don’t do anything automatically unless you’re in “Ask to connect” mode. In this case GlassWire automatically blocks new connections until you allow them.
GlassWire works fine with VPN software. We don’t do something to PIA VPN at all, but you can do so on our firewall, or you can turn on “Ask to connect” and block them, or “Block all” and block everything on your PC from calling out.