Android Firewall

This screen allows to configure Android integrated firewall when available (see here for more information)

At the top you can block all applications trying to use WiFi or APN (mobile data). Doing so the checkboxes below become check marks (instead of crosses) to enable access for specific apps.

Configuration is applied immediately (more precisely when exiting the tab, one way or another). To make it persists accross reboots, make sure to enable the on-boot button in the top-right corner.