> - Control external monitor sound volume. There are buggy paid and open source solutions, but they all trigger all kind of bugs with sound and macOS itself.

For me this is one of the most annoying missing feature of macOS, while there are 3rd party apps, I'd want to have it without installing anything extra. But as we know it hard (if not impossible) that Apple implements this feature for other than their supported devices (that is mostly their products and maybe some of the 3rd party displays that they sell in their official web store).