Thank you Yves.
There is no monitor detected, at all, by the chip in the dock.
For the DisplayPort monitor, I do see "hotplug" detection, then the monitor EDID being read and saved in the .edid file. However, there is nothing for any other head. That leads me to believe there is a fault in the hotplug detection hardware: no monitor is detected as getting plugged in, so the dock doesn't even try to read what's connected.
Is it a single dock behaving like that? If so, once you have verified it is not a cable fault, I would recommend contacting the manufacturer, Dell, to discuss a replacement. I suggest you copy this message so they don't waste time looking at the driver...

I purchased a 2nd DL3100 to test it wasn't a faulty unit.
But the new one did the exact same thing.

Have you tried with another monitor or HDMI cable?

I don't expect you to have a different behaviour on any other computer as the firmware does not see any monitor.

I'll give that a try if a other brand monitors might change something.

I seem to have a similar issue with this dock. Question: have you tried plugging it into a USB 2.0 port?

For me, the USB 2.0 port works but the USB 3.0 doesn't detect the dock.