I was able to test this with a Windows 10 machine and the latest available drivers (10.1 M1) and I was able to run native resolution 5120x1440, even at 70Hz.
screenshot Windows.jpg
D6000 was connected via USB-C and screen via Displaylink. That means, the dock can actually handle it and it seems that this is something that needs to be fixed in the Linux driver.
Is there any chance that technical support can look at this? I tried to email but it bounced back. I would be more than happy to test a possible fix.
Thank you