How to edit Nextclouds config.php file with a texteditor?
You can edit Nextclouds config.php file directly from the host with your favorite text editor. E.g. like this:
sudo docker run -it --rm --volume nextcloud_aio_nextcloud:/var/www/html:rw alpine sh -c "apk add --no-cache nano && nano /var/www/html/config/config.php". Make sure to not break the file though which might corrupt your Nextcloud instance otherwise. In best case, create a backup using the built-in backup solution before editing the file.
The name of the container may vary depending on the setup, but I can’t say without knowing your system. Maybe it helps if you post the output of ‘docker ps’ here.