Ok, had my wife send me the file from my network

networks:
  main-network:
    name: ${COMPOSE_PROJECT_NAME}
    attachable: true
    ipam:
      driver: default
      config:
        - subnet: configure
          ip_range: this
          gateway: yoself

services:
  # Gluetun - <https://github.com/qdm12/gluetun>
  gluetun:
    image: qmcgaw/gluetun
    container_name: gluetun
    networks:
      - main-network
    cap_add:
      - NET_ADMIN
    environment:
      - PUID=${PUID}
      - PGID=${PGID}
      - TZ=${TZ}
      - VPN_SERVICE_PROVIDER=custom
      - VPN_TYPE=wireguard
      - VPN_PORT_FORWARDING=true
      - VPN_PORT_FORWARDING_PROVIDER=protonvpn
      - WIREGUARD_ADDRESSES=use your own
      - WIREGUARD_ALLOWED_IPS=0.0.0.0/0
      - WIREGUARD_PRIVATE_KEY=nope
      - WIREGUARD_PUBLIC_KEY=69420
      - WIREGUARD_DNS=
      - VPN_ENDPOINT_PORT=
      - VPN_ENDPOINT_IP=
    volumes:
      - ${DOAPPDAT}/gluetun:/gluetun

I left in the wireguard stuff without my details because for me Gluetun refused to work when setting the exact same info to wg0.conf, so I define it in my compose

Then, services that rely on gluetun go below and look like:

# qBittorrent - <https://hub.docker.com/r/linuxserver/qbittorrent>
qbittorrent:
  container_name: qbittorrent
  network_mode: container:gluetun
  image: lscr.io/linuxserver/qbittorrent:latest
  depends_on:
    gluetun:
      condition: service_healthy
  restart: unless-stopped

Works perfectly when I run it through portainer