How to set static ip when a container use network_mode: service:<container>

I am struggling with networks and Docker/docker-compose. Use case :

• I am using Transmission as a client Torrent, in network_mode with a wireguard VPN for privacy.
• Next to it, I have a Jackett container and a Sonarr container for automatisation. The problem is my local ip of my Wireguard container(showing itself in the VPN container) keep changing every time I reboot, but I need it to be permanent for Jackett/Sonarr. The think is I am using network_mode: service:container to use my VPN with my Transmission client, and I have no idea how to make both of my container (VPN and Transmission) with static IP.

I am doing a bridge between Jackett, Sonarr and VPN to let them able to communicate between them.

Do you have any idea how to make their IP statics ? Or, in a first half, VPN with a static local ip ?

version: "2.1"
services:
  plex:
    image: plexinc/pms-docker
    container_name: plex
    environment:
      - TZ=Europe/X
      - PLEX_CLAIM=X
    volumes:
      - /home/X/docker/plex_config:/config
      - /home/X/docker/plex_transcode:/transcode
      - /media/data:/data
    ports:
      - 3240:32400
  transmission:
    image: ghcr.io/linuxserver/transmission
    container_name: transmission
    depends_on:
      - vpn
    network_mode: service:vpn
    environment:
      - PUID=1000
      - PGID=1000
      - TZ=Europe/X
      - TRANSMISSION_WEB_HOME=/flood-for-transmission/
    volumes:
      - /home/X/docker/trans_config:/config
      - /media/data:/downloads
      - /media/data/watchTorrent:/watch
   # ports:
     # - 9091:9091
     # - 51413:51413
     # - 51413:51413/udp
    restart: unless-stopped
  vpn:
    privileged: true
    image: cmulk/wireguard-docker:buster
    volumes:
     - /etc/wireguard/conf:/etc/wireguard
    networks:
      - net
      - linked
    ports:
      - 5555:5555/udp
      - 9091:9091
      - 51413:51413
      - 51413:51413/udp
    restart: unless-stopped
    devices:
      - /dev/net/tun
    sysctls:
     - net.ipv6.conf.all.disable_ipv6=0
    cap_add:
     - NET_ADMIN
     - SYS_MODULE
  sonarr:
    image: ghcr.io/linuxserver/sonarr
    networks:
      - linked
    container_name: sonarr
    environment:
      - PUID=1000
      - PGID=1000
      - TZ=Europe/London
    volumes:
      - /home/X/docker/sonarr/data:/config
      - /media/data/Series:/tv #optional
      - /media/data/:/downloads
    ports:
      - 8989:8989
    restart: unless-stopped
  jackett:
    image: ghcr.io/linuxserver/jackett
    container_name: jackett
    networks:
      - linked
    environment:
      - PUID=1000
      - PGID=1000
      - TZ=Europe/London
      - AUTO_UPDATE=true #optional
      - RUN_OPTS=<run options here> #optional
    volumes:
      - /home/X/docker/jack/conf:/config
      - /media/data/:/downloads
    ports:
      - 9117:9117
    restart: unless-stopped
networks:
  net:
  linked:
    driver: bridge

Plus, when I am looking for the IP inside Tranmission with this command :

docker inspect -f '{{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}' container_id

it returns nothing. But with the VPN container, it returns me 2 local IPs. Exemple : 192.168.224.2192.168.208.2

Thank you for your time !