qBittorrent has an option to define the WEBUI_PORT. If you want to access it on say, port 8585, set this environment variable to WEBUI_PORT=8585. Then in gluetun, continue to reference it as you do above. Hope this helps. registry.hub.docker.com/r/…/qbittorrent

  qbittorrent:  
    container_name: qbittorrent  
    image: linuxserver/qbittorrent:latest
    environment:
      - WEBUI_PORT=8585
    restart: unless-stopped
    network_mode: container:vpn  
    volumes:  
     - /docker/appdata/qbitorrent:/config