According to @denNorske, the “Filtering disabled container” is shown for each container that is not in scope for auto-discovery, which is normal for all nextcloud-aio containers.
You can see all running containers with the command docker ps and for each of your networks, e.g. the network proxy, you can see which containers are connected by executing e.g. docker network inspect proxy.
With the help of @denNorske the problem described in https://help.nextcloud.com/t/nextcloud-aio-with-traefik-gives-404-on-public-domain was eventually solved by detailed inspection of traefik.log before and after changes to the traefik configuration, and finally by testing the domain using curl -vL [your domain]. This revealed that the domain name was misspelled in my traefik configuration, as I had replaced https by websecure in too many places.