> is it, or is there a re-driver?

How would I go about verifying that? I've never installed any driver for the dock, and the DP-connected screen works during early boot. Linux recognizes it as DP-X-Y. I've never had the curiosity of plugging in the HDMI port under Linux.

On Windows, it recognizes 3 screens when both DP and HDMI are connected (the third being the internal laptop display).

I know there's a similar HP dock, the G2, that does say it has DisplayLink, whereas this one doesn't.

> the other 2 are for DP-HDMI convertor and DP connector. seems like only 1 of HDMI or DP should work at 1 time.

If it's a USB 3.2 2x2, shouldn't that be able to handle one 4k@60Hz stream per lane, thus supporting two 4k@60 displays at the same time?

> Linux recognizes it as DP-X-Y.

That's interesting, I've always seen Linux recognizing DP ports as only DP-X in xrandr. So my first guess would be that what you have within the dock is a something like a DP MST hub, to split the single DP port into two, and then one of these two ports goes into the active converter to HDMI (perhaps in the same chip), while the other is exposed as the DP socket.

You may be on to something, especially since I seem to remember people having MST displays complaining about wonky support.

Another fun fact: the laptop I'm typing this on shows 4 DP connections (DisplayPort-0 through 3), one HDMI-A-0, one eDP. There's no dock connected to it right now. When I was using the Chinese dock with a DP monitor, one of the four was showing up as connected.

The PC only has two USB-C connectors and one HDMI. So, I guess it expects to be able to drive two displays per USB-C port.