I'd prefer if the parameter was named args and you pass it a JS object, like

increaseMicrophoneVolume({showOsd: true})

Avoids boolean trap. Again, same in the old code and to be fixed separately.

Doesn't that block introspecting?

I know it's in the old code but should be fixed later I guess

Yeah, that looks better. Will change it in next commit.

It's generated from XML, so it does not introspect.
But indeed should be constructed just once.