What is 192.168.100.7? What IP are you pinging from? Which adapter is that subnet on? I recommend not using Net networks in VBox unless you have no choice, it makes everything much more complex. Steve

So your on-prem Webserver is also running as OpenVPN client which is connected to your gcloud pfSense? You are only running this one pfSense? What is your OpenVPN mode? -Rico

pfSense should not have a LAN gateway. If you have that set on the LAN interface remove it. Then go to System > Routing and make sure the WAN gateway is set as default. The fact you are able to reach the webgui shows it must be working to some extent. Steve