The thunderbolt_stream driver exposes /dev/tbstreamX devices on each host of a directly-connected USB4/Thunderbolt cable. From there data can be transferred using regular file-system operations, e.g. you can dd or cat from one system to another or similar commands.

This I like! Back when I started transferring stuff between computers, this was exactly what I expected to hallen when connecting two computers via USB. It was disappointing to find out only certain USB cables supported it. Maybe there were even kernel modules for it, but USB4stream will be so much easier.