Trying to get BalenaSound working with Raspberry Pi 3B. I have found that after a reboot, I have to refresh Airplay service in the cloud app before the device shows up as an option for Airplay. Otherwise it does not show up at all or shows up intermittently and cuts out after a few seconds just like the bluetooth does on the 3B. After refreshing, Airplay functions properly, but this has to be done every time the Pi reboots or when a variable is altered.
As an aside, I noticed that the official guide lists the Raspberry Pi 3B as recommended alongside the 4B in the “Hardware Required” section. However, the troubleshooting guide shows that the 3B has issues with bluetooth connectivity such that the recommended workaround is to use a USB dongle. I would suggest this Pi model not be recommended alongside the Pi 4 in the getting started guide given this issue.