Adding Service Changed Characteristic to Generic Attribute Service?

Ok, just filed an issue https://github.com/espruino/Espruino/issues/1966

I bet it's related to the SC Control Point which at least I can test on the Pixl side.

I'd still be a bit unsure about that. I reckon it'd be worth trying some of the other things first as I've never known anything to use the SC control point other than Nordic DFU