How to enable an unsupported HP Thunderbolt dock on macOS Catalina
Super smug answer, I'll add some less smug information - I have both HP Elite and G2 120W TB3 docks which worked 90% perfectly in 10.15 (with the unsupported patch installed) - sound, USB3.0, thunderbolt passthrough/USB-C video, networking and charging. The only thing that didn't work was the Displayport based outputs (and VGA I assume but I never tested that). They're all based off pretty standard chipsets and don
t need any drivers is MacOS.
So yes everything you say is correct but if you jump across to Bootcamp it all works so its all in Apples court really.
The unfortunate current situation is that from what I can tell there is no patches available for Big Sur to enable Thunderbolt so on my Elite I only have USB-C pass through video (quite happily doing 4KP60) and charging.
Lets hope something comes out in the future as there are lots of the HP docks turning up on eBay that are exlease and never used.