Before USB 4, USB-C spec itself say "see also USB 3.1" for USB hubs and disallow passing through Alternate Modes (e.g. Thunderbolt/DisplayPort) or Accessory Modes (e.g. audio dongle) which vastly limited the usability of USB-C port. USB 4 introduces a new discovery protocol with added support for passing through Alternate Mode in USB-C spec (as long as downstream is also USB 4).