Same problem. Just installed 11.2.1 - No Joy.
I'm running a Macbook Pro 2016 - 2019
32GB ram 4TB.
I'm connected to a J5Create JCD543. Via USB-C
2 DELL SE 2719HR displays.
Also tested on a 2019 Macbook Air. - No joy
Prior to Big Sur, my set up was solid.
Work Arounds: As of Feb 16 2021
Option 1: j5Create just launched a driver. But...well... as of now, it's not useable. It works. Kind of... but it's DJTVirtualDisplayAgent and some other USB virtual software that needs to be approved by security. It enables the second display, but with a 1 or 2 second screen lag. So any interaction with items on that display are slow. Like using Virtual PC in the 1990's. Maybe they will improve this.
Option 2: Use 2 USB-C ports. So, one cable goes into the j5Create hub and the second goes into an HDMI to USB-C adapter. Not the end of the world, but does require an extra USB-C port. results in normal use of 2 displays.
Option 3: I tried other hubs (prices may have changed since posting this.)
USB-3 Hub 123.99
https://amzn.to/3jV4aYp (both displays worked, but requires a special USB-C dual port cable) - returned
Portable USB-C hub pro $59
https://www.amazon.com/dp/B0855GZ7PT (both displays worked, but also requires 2 ports, plus, it's a short cable, all cables must be visible on the table. I'm sure you know what I mean.. messy. - returned
Docking Station OKX $149
https://www.amazon.com/dp/B08HLXLW1Q (Yes, best choice so far. only requires 1 cable and has lots of ports. BUT It does require a driver.
https://www.displaylink.com/downloads
It's still a hack. requires you to be logged into the user account that you have installed the software. So, that means 1 display will be active while rebooting, up until you actually log in, then after about 15 seconds, it launches the second display. No lag, it works well as a work around. This one I'm keeping.
Oh, to save you time, I tried installing this displaylink software to use with other hubs. No dice, it looks for it's own hardware. sorry... (as of the time of this posting. Maybe that will change)
Summary:
I kept the OKX docking with displaylink for my home office. It's nice and clean, with the hub hidden and a 1 simple cable into my USB-C port (also provides power). Nice... but cluncky when rebooting. Must wait for software to load.
At work, I kept the j5Create. 1 USB-C cable from the hub, and all my devices are neatly tucked away. Requires a second HDMI-USBC cable to power 2 monitors, and takes 2 ports. Hopefully Apple will figure out the conflicting software or someone will find a terminal hack to help us all out.
Ethan-
