MacOS Big Sur already contains device IDs for AMD RX 6800, 6800XT, and 6900XT among others. However the driver classes for these GPUs are still missing.
Remember that macOS and all other PCI-compliant operating systems always scan the PCI bus for all devices attached to the system, query the Device and Vendor IDs from each device, then look for drivers that support those IDs.
In MacOS this is typically specified in a kext info.plist by a property called IOPCIPrimaryMatch. Because there are a large number of kexts in the system and each kext matches different sets of device IDs, there arises the concept of the “kernel cache”.
If you recall, the “kextcache” command is applied to /L/E and /S/L/E that both contain kexts. The kernel cache builds an optimized driver dependency tree that is used not only to match device IDs to their kexts, but also to determine which kexts depend on which sub-kexts.
For example, WhateverGreen is a plug-in for Lilu, so it depends on Lilu. Although we don’t install Lilu and WEG in /L/E any longer and therefore they are omitted from the kernel cache, they are nevertheless a good example of a dependency relationship.
So the fact that PCIe device IDs for all AMD 6000-series variants are already present in Big Sur is, to say the least, interesting...