The problem is the smbclient packages need to be installed inside the Docker container. Installing it on the Docker host OS won’t work. I don’t know why it isn’t included. It would save a lot of people a lot of trouble if they included the two little packages.
You can open a shell in the container using
docker exec, then install with apt. This is only a temporary fix because next time you pull an updated container image, it won’t have smbclient again.A more permanent fix is to build the container image yourself. Docker-compose can do this mostly automatically once you set it up.
You can find out how to do this here:
docs/nextcloud/README.md at master · docker-library/docs · GitHubI also cover it briefly in my guide:
https://help.nextcloud.com/t/howto-ubuntu-docker-nextcloud-talk-collabora/76430
Ahh…
Yeah makes no sense that thes dont include this in the image already…
Thanks for your time and explanation. Now i am outside but later in evening i will read and try that. I never did build a image myself, but can you tell from experience if it is hard for beginners or not? I mean building a docker container is one thing but an image?..sounds hard 
I will report back here if it worked or not or if i have problems