In a post about how macOS’s boot volume structure has been updated, Howard Oakley explains that the pkg directory was added to the Data volume in macOS 26.4, but not added to the root of the Signed System Volume until 27.0. He also notes that this is sort of a big deal.
The weird thing is, as far as I can tell, no one seems to know what this new directory is for! It’s odd that Apple would update their filesystem structure, add it to everyone’s PATH, and there not be some explicable reason.