You run a gluetun container and a qBittorrent container on which you set the “network mode” to the gluetun container. Then you put your *arr software and the gluetun container in the same (virtual) network so they can communicate internally. All containers using gluetun as their “network mode” have their ports available on the gluetun container. You can also put the qBittorrent container in your virtual internal network but then you have to make sure that the network is marked as internal to avoid traffic leaking.