@thislooksfun, welcome to the forums! The first thought that occurs to me is whether you were testing it with balenaOS v2.41.0, because of these recent issues:
- Raspberry pi headphone jack no longer works with latest OS
- https://github.com/balena-os/balena-raspberrypi/issues/379
If so, the recommendation is to upgrade to v2.43 or later, or downgrade to v2.38 (downgrading currently requires re-flashing the SD card). Otherwise, I could also suggest a couple of other sound-playing projects for testing / debugging:
Let us know how you get on!