The best list of VFS folder mapping that I can find is from the days of the desktop bridge:
Behind the scenes of the Desktop Bridge - MSIX | Microsoft Docs
This is clearly an incomplete of the mappings supported within MSIX. Some additional folders can be seen in the mappings of the PSF/FileRedirectionFixuup (PathRedirection.h), but those exist because I ran into cases created by the packaging tool and added them myself. It is unlikely that this represents all possible mapping implemented by MSIX.
It would be good to have an updated official list.