Was it Nextcloud or Nextcloud All in One? I've just realised that the Nextcloud docker image I use is maintained by Docker, not Nextcloud. It's this one: https://hub.docker.com/_/nextcloud/
I use Docker-compose and even the examples there don't have any socket access.
The all in one image apparently uses Traefik, which seems weird to use an auto configuring reverse proxy for an all in one image where you know the lay of the land. Traefik requires access to the docker socket for auto configuration. But you can proxy the requests to limit access to only what it needs if you really want to use it.