With a lot of help from SicklCodes I've finally got my Displaylink working under 5.9.10...
I had previously followed the patch from post 2, but this did not appear to work... Among trying lots of different fixes, it seems that a patch from SickCodes' repo seemed to bring it all together...
git clone
https://github.com/sickcodes/evdi.git
cd evdi
git checkout -f master
make
sudo make install
It would be great if this could be included with the current DisplayLink offering
It also seems as though the displaylink-driver.service was not starting automatically., but was found to be present from typing 'systemctl status display' and tapping tab twice (without hitting enter).
You can then test whether it will start with 'sudo systemctl start displaylink-driver.service'
This worked for me to bring my additional 2 displays (1xHDMI and 1xDVI) from my DisplayLink adapter... I also had the HDMI straight from my Ryzen 7 laptop (with Nvidia MX350) working in parallel with the DVI from the DisplayLink alongside the laptop screen...