I gave up trying after numerous of attempts to reinstall DL drivers, changing settings and manually looking to remove any old DL files before reinstalling the drivers, rebooting each time etc. Nothing worked until today when I started again DL manager (to collect logs for a DL rep who's asked me to do run the app first) and
this time it magically worked again! Fortunately, I cannot reproduce the problem anymore and won't even try to install again the LOGIN SCREEN EXTENSION add-on described at
https://support.displaylink.com/know...ntroduction-in.
EDIT: At one point while having 2 vertical DL monitors on (not using them really because can't rotate) my native external monitor connected via UGREEN hub/adapter lost connection and was unable to reconnect. I tried connecting the monitor via another UGREEN USB-C to HDMI dedicated adapter but no joy. A reboot restored the connection - not sure if it was DL that caused it or OS X Big Sur 11.0.1.
Cheers,
David