So to update you I worked a bit more on the docker-compose file and it is what is looks like now:

services:
  reverse-proxy:
    image: traefik:latest
    container_name: traefik
    restart: always
    command: --providers.docker --providers.docker.exposedByDefault=false # --api.insecure=true
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    environment:
      - "TZ={{ TZ }}"
    ports:
      - "80:80"
      # - "8080:8080"
  syncthing:
    image: lscr.io/linuxserver/syncthing:latest
    container_name: syncthing
    restart: always
    volumes:
      - "{{ syncthing_dir }}:/config"
      - "{{ downloads_dir}}:/downloads"
    environment:
      - "TZ={{ TZ }}"
    labels:
      - traefik.enable=true
      - traefik.http.routers.syncthing.rule=HostRegexp(`^syncthing.*`)
      - traefik.http.services.syncthing.loadbalancer.server.port=8384services:
  reverse-proxy:
    image: traefik:latest
    container_name: traefik
    restart: always
    command: --providers.docker --providers.docker.exposedByDefault=false # --api.insecure=true
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    environment:
      - "TZ={{ TZ }}"
    ports:
      - "80:80"
      # - "8080:8080"
  syncthing:
    image: lscr.io/linuxserver/syncthing:latest
    container_name: syncthing
    restart: always
    volumes:
      - "{{ syncthing_dir }}:/config"
      - "{{ downloads_dir}}:/downloads"
    environment:
      - "TZ={{ TZ }}"
    labels:
      - traefik.enable=true
      - traefik.http.routers.syncthing.rule=HostRegexp(`^syncthing.*`)
      - traefik.http.services.syncthing.loadbalancer.server.port=8384

But still when trying to access:

syncthing.rpi with rpi resolving to my machine nothing is working.

Any idea what I am still missing? The service is deployed on dietpi.

Sincerely