Thank you, @ESSEDIA, for your pointer. I tried many things from that site, and other stuff inspired by that site. Nothing worked.
I decided to do a clean 19.04 install on my Dell G5 5587, with D3100 docking station. The first thing I did, after the clean install was done, was to install the DisplayLink driver v5.1.26. And, guess what, it now works like a charm.
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