Thanks for sending the file. What you need to do is add the label to the service which informs the supervisor to mount the kernel module directory into the container. This label is io.balena.features.kernel-modules and the documentation is available here: https://www.balena.io/docs/reference/supervisor/docker-compose/#labels.
You may also need to set the privileged flag for the container which is doing the modprobe, using privileged: true in the service definition.