Mount net share with cifs within a container using docker-compose

Question

I have a docker-compose under windows with cap_add and privileges set in order to mount a windows net share in the dockerfile (running a debian) by using cifs. During the build I always get "Unable to apply new capability set". However, if I get with the bash into the running container I can mount without any problem.

Here is the dockerfile relevant code:

RUN apt-get install cifs-utils -y
RUN mkdir /opt/shared
#RUN mount -v -t cifs  //10.20.25.14/external /opt/shared -o 
"user=username,password=mypass-,domain=mydm,sec=ntlm"

and this is the docker-compose part:

  anaconda:
    privileged: true
    image: piano_anaconda:latest
    security_opt:
      - seccomp:unconfined
    cap_add:
      - SYS_ADMIN
      - DAC_READ_SEARCH
    build:
      context: .
      dockerfile: dockerfile_anaconda

I have read this as well but it did not really help to mount within the docker file. What am I missing here? Thanks in advance to all for your help.