Inspiron 15 7506 and WD19TB Thunderbolt Dock - external monitor doesn't work under Linux

Hi folks,

I have a very new Dell Inspiron 15 7506 with Ice Lake CPU and Thunderbolt 4 port running Manjaro Linux (based on archlinux) with kernel 5.8.18-1.

I also bought the Dell WD19TB Thunderbolt 3 dock and connected it to the Inspiron.

The Ethernet, USB ports and power delivery of the dock work well. The only thing I can’t get to work is my external monitor. When I connect it via HDMI or Display Port of the dock I get a window where I can choose which monitor or both together or mirrored.

But none of these choices gets the external monitor to show anything, it just stays black.

I think I have to mention that my monitor is a rather old device, a 10 year old LG that has only VGA and DVI connectors. The connection to the HDMI or Display port of the dock is established via a DVI to HDMI adapter cable.

Do you have any ideas what I can try next to solve this problem?

Thanks in advance