I made a slight change to the M5UnitSynth library so that it will work with the ESP32-C6. I created a pull request, but it may never be approved, so here is a link to the modified library https://github.com/kd8bxp/M5Unit-Synth/tree/serial

I also added Fur Elise for the M5StickC and the M5NanoC6. Hopefully someone finds it helpful.

PS. I have no idea why M5 requires the M5Unified, and M5GFX libraries, they aren't being used for this library at all. Which means, (I am not sure)- This really should work with any esp32 micro-controller, and I've tried it with a few different ones.