afwall

I have heard good things about this one. But i think this one of those no root firewalls that uses the vpn, so I figure this means I can't use a VPN at the same time. An alternative android root only option is afwall+ which allows blocking on lte, WiFi, lan, and VPN separately, and script access to iptables. Not sure how actively developed it is, but it seems to work ok. *edit: Seems to still be active, open source, and available on fdroid too. https://github.com/ukanth/afwall

Sadly all real firewalls need root. I was using AFWall+ for a long time it has neat controls for every app to allow or deny Wifi, Cell or LAN (if you have). It is a iptables/nftables frontend so you can customize the rules to your heart's content: https://github.com/ukanth/afwall Works from Android 2+ Without root only VPN solutions like Adguard are available. EDIT: if you want neat stats: Glasswire has an Android version. I have only used the beta so I have no idea about its current state. Might be worth checking out though.