People who use Thunderbolt think of Thunderbolt hubs which is another name for a desktop dock or a desktop card reader.
Thunderbolt Hubs are the traffic routers or switches inside Thunderbolt devices for managing USB, PCIe, DisplayPort, Ethernet, etc. in the device and in daisy-chain.
Thunderbolt 1, 2, 3 did not make it important for the consumers to know about Thunderbolt Hubs.
Thunderbolt 4 changes Thunderbolt Hubs!
(Insert Sonnet video)
Thunderbolt 4 Hubs allow for PCIe x4 to pass through to any of the three continuation ports still supporting up to six devices along the bus.
Thunderbolt 4 Hubs allow for PCIe x1 (750 MBps) to be used by the device.