I didn't believe you, then I went and checked.
https://www.cnet.com/news/usb-4-will-resurrect-those-useful-...
Apparently all the hubs that have multiple USB-C ports are running USB 2 over them, or you can just use them for power delivery.
I am suddenly very happy that none of my other devices except for my USB-C hub, actually uses USB-C, I'd be limited to the ports that came on the computer!
Thunderbolt docks can do it, they just run multiple USB controllers on board, one for each port, but indeed, it USB-C 3.1 as it stands today doesn't support hubs.