Alright, the kernel modules are built now using this Dockerfile.template file:
FROM balenalib/%%BALENA_MACHINE_NAME%%-debian-node:latest
RUN apt-get update && apt-get install -y curl wget build-essential libelf-dev awscli bc flex libssl-dev python bison
COPY . /usr/src/app
WORKDIR /usr/src/app
#ENV CROSS_COMPILE aarch64-linux-gnu
ENV VERSION '2.50.1+rev1.prod'
#ENV VERSION '2.29.0+rev1.prod'
RUN ./build.sh raspberrypi4-64 $VERSION matrixio-kernel-modules/src
#RUN ./build.sh --list
CMD ./run.sh
The next step is combining this with my existing repo and testing to see if the microphone is now working. I will post the outcome here