Has anyone already implemented something like this and can provide code snippets? The goal is to trigger the smartphone camera with volume-up event.

I'm not aware of anyone implementing ble hid. It's something I'm interested in myself. If you manage to make it work let us know

Got it to work: - test-camera.toit, - ble-camera.toit https://github.com/kaxori/genesis/tree/main/src

Nice!