Problem described here (for those who might come to this thread due to same issue):
https://www.displaylink.org/forum/sh...ad.php?t=67537
Tried the fix explained here:
https://displaylink.org/forum/showpo...9&postcount=19
Tried the fix with both 5.4 kernel (default in Mint 20.1) and a 5.8.x kernel (via Update Manager). Neither made a difference. Still just blurry lines in correct resolution.