No audio out with Balena Sound on RPi3B+

There’s actually an issue open for this - it seems to be an issue with the 64 bit OS running on a Pi 3. There’s a comment there that solved the issue for me - remove the vc4-kms-v3d overlay from the device configuration and reboot. That way you won’t need to install the 32 bit OS (actually I couldn’t find the 32 bit option when trying to add a device in Balena Cloud).