_Report from Big Sur public beta 20A5364E (latest public beta as of 2020-09-09)_
Karabiner seems to be in some kind of crashing loop.
Here is a screenshot of the log:

Those error messages just keep repeating.
Here's a Screencast of the log next to macOS' preference pane for the keyboard.
You can see that the dropdown for an alternative keyboard appears very _very_ briefly as it flashes in the System Preferences window. I believe this shows that it is activating, but then immediately crashing.
I have tried rebooting my Mac and I have uninstalled and reinstalled Karabiner Elements.
Thank you for feedback!
I released new version (12.93.0) which fixed a bug. Please confirm it.
https://karabiner-elements.pqrs.org/docs/macos-big-sur/
Thank you for feedback!
I released new version (12.93.0) which fixed a bug. Please confirm it.
https://karabiner-elements.pqrs.org/docs/macos-big-sur/
Confirmed to work on MacOS Big Sur Beta 6! Thanks so much!
Yes! This works. Thank you very much.
Most helpful comment
Thank you for feedback!
I released new version (12.93.0) which fixed a bug. Please confirm it.
https://karabiner-elements.pqrs.org/docs/macos-big-sur/