@toochevere Indeed, that works! I used the balenablocks/audio code in version 0.1.13 on Github, before moving from Buster to Alpine: v0.1.13 · balenablocks/audio@8ef686a · GitHub
I copied the relevant code in Dockerfile.template, the files in audiopulse/ and udev/, and adjusted the code in the template to my case, such as WORKDIR, ENTRYPOINT and CMD.
It seems to work as before. Thanks a lot!