But how does the app even work? If it changes the host file, I suppose it has to be a default/system app to get the required rights.
If it uses an internal DNS, I think it isn’t possible to block ads this way on Android phones due to Google automatically adding their dns BEFORE even the DHCP provided ones?
As an example, I have a Pihole at home on 192.168.0.250, but my Android phones automatically puts Google DNS before that, unless I use a VPN (In my case a Wireguard that point to my ISP Router), in which case the Google DNS isn’t added.