Hey guys, I'm also one of the few which got an 6800XT. For me its the same - Big Sur working but no acceleration. I'll try also some stuff today maybe we get closer to a working system...
There may be a way to edit the info.plist if the 6000.kext to slow it to run on the Navi 10 drivers.
You have to go into recovery and disable the security screenshots and then disable gatekeeper.
If someone has a spare drive for testing it would be nice to see if you can get metal.
Here is a link to disable system file protection which blocks editing of kexts.
Warning: This may break your BS installation. Do this as an experiment on a spare drive. You can also make the changes to the EFI using a USB install stick.
How to disable system file protection and making free access to all folders in Big Sur? these commands no longer works here:( sudo mount -uw / sudo killall Finder