I can't tell what Linux does but USB4NET works without a hitch through USB4 hubs.
To go technical we need to check the USB4 System Overview. https://www.usb.org/sites/default/files/D1T1-3%20-%20USB4%20... to find four types of Protocol are mapped to USB4: USB3 Adapters, DP Adapters, PCIe Adapters, Host Interface Adapters. We are all familiar with USB3, DP, PCIe but what is a "Host Interface Adapter"?
Now we need to open another document https://www.usb.org/sites/default/files/D2T1-3%20-%20USB4%20... to find "Provides parallel communication channels: Control Packet Routing, Host-to-host tunneling" under the Host Interface section. It's Host-to-host tunneling we want.
Finally, go to page 55 of this PDF and see Path Terminology -- most importantly you can see there can be any number of Path Segments.
So to recap: The so called Thunderbolt networking is now called USB4NET, it is provided by the Host Interface Adapter, and it can travel over any number of routers. (In the first doc, you can find routers are the fundamental block of USB4, host, router, device are all routers and in this sense they are the same.)
To go technical we need to check the USB4 System Overview. https://www.usb.org/sites/default/files/D1T1-3%20-%20USB4%20... to find four types of Protocol are mapped to USB4: USB3 Adapters, DP Adapters, PCIe Adapters, Host Interface Adapters. We are all familiar with USB3, DP, PCIe but what is a "Host Interface Adapter"?
Now we need to open another document https://www.usb.org/sites/default/files/D2T1-3%20-%20USB4%20... to find "Provides parallel communication channels: Control Packet Routing, Host-to-host tunneling" under the Host Interface section. It's Host-to-host tunneling we want.
Finally, go to page 55 of this PDF and see Path Terminology -- most importantly you can see there can be any number of Path Segments.
So to recap: The so called Thunderbolt networking is now called USB4NET, it is provided by the Host Interface Adapter, and it can travel over any number of routers. (In the first doc, you can find routers are the fundamental block of USB4, host, router, device are all routers and in this sense they are the same.)