How to prevent apps from using WiFi network?

I would like to prevents all app except one (which I use it in foreground) to use WiFi network. The phone is not rooted so the root firewall are not suitable, and also I don't want to use firewall which create VPN connection. I have tried how-to-restrict-background-data-for-metered-wi-fi-networks-on-android but when I check the network traffic of the device it contains closed app traffic also.