hey @holg
Can you try to use the raspbian base image instead?
You should change it to FROM balenalib/rpi-raspbian
You might have to install nodejs in the base image.
You can install packages using our install_packages utility. tvservice is already included in the base image and you can install cec utility using RUN install_packages cec-utils
We have colleagues who have been successful in using both cec-utils and tvservice.
Hope this helps