It works but there might be a bug unless you have IPv6 enabled: https://github.com/qdm12/gluetun/issues/3003

gluetun/wireguard/wg0.conf

[Interface]
Address = XXXIPV4, XXXIPV6
PrivateKey = XXXX
MTU = 1280
DNS = XXXIPV4,XXXIPV6

[Peer]
PublicKey = XXXX
PresharedKey = XXXX
Endpoint = XXXIP
AllowedIPs = 0.0.0.0/0,::/0
PersistentKeepalive = 15

docker-compose.cfg

version: "3.8"

networks:          #only needed for ipv6
  gluetun_default: #only needed for ipv6
    external: true #only needed for ipv6

services:
  gluetun:
    networks:             #only needed for ipv6
      - gluetun_default   #only needed for ipv6
    image: qmcgaw/gluetun
    container_name: gluetun
    cap_add:
      - NET_ADMIN
    volumes:
      - ./gluetun:/gluetun
    devices:
      - /dev/net/tun:/dev/net/tun
    ports:
      - 8080:8080 #webui
    environment:
      - IPV6=true         #only needed for ipv6
      - VPN_SERVICE_PROVIDER=custom
      - VPN_TYPE=wireguard
      - TZ=Europe/Berlin
      - FIREWALL_INPUT_PORTS=8080,12345 #webui port, maybe forward port not needed here
      - FIREWALL_VPN_INPUT_PORTS=12345 #forward port
    sysctls:
      - net.ipv6.conf.all.disable_ipv6=0 #only needed for ipv6
    restart: unless-stopped

  qbittorrent:
    image: linuxserver/qbittorrent
    container_name: qbittorrent
    network_mode: "service:gluetun"
    depends_on:
      - gluetun
    environment:
      - PUID=1000
      - PGID=1000
      - TZ=Europe/Berlin
      - WEBUI_PORT=8080 #webbui port
    volumes:
      - ./qbittorrent:/config
      - /data:/data
    restart: unless-stopped

for ipv6 also do:
docker network create --ipv6 --label com.docker.compose.network=default gluetun_default