FTA there seem to be at least 2 problems:

"the Pi has problems with cache coherency on the PCI Express bus beyond 32-bits. And many (well, all nowadays) of the drivers expect that to function."

Yeah, that's a problem.

"there were issues with the BAR (Base Address Register) space allocated on the Pi's OS."

From the GitHub link:

# The default BAR address space available on the CM4 may be too small to allow # some devices to initialize correctly. To avoid 'failed to assign memory'

These don't look like implementation quirks, they are just flat-out errors.