HS1TX(P) of the source is connected to HS1RX(P) of the sink.
The cable is actually a crossover cable, it swaps all receive and transmit lanes e.g.
This is the pinout for both sides of the connector, source side and sink side. Thunderbolt 4: 4× PCI Express 3.0, DisplayPort 2.0, USB4 Thunderbolt 3: 4× PCI Express 3.0, DisplayPort 1.2 (2 streams), USB 3.1 gen. Thunderbolt 2: 4× PCI Express 2.0, DisplayPort 1.2 Thunderbolt 1: 4× PCI Express 2.0, DisplayPort 1.1a Thunderbolt 3: 40 Gbit/s bidirectional, 80 Gbit/s one way Thunderbolt 1: 2 channels, 10 Gbit/s each (20 Gbit/s in total) Via DisplayPort protocol or USB-based external audio cards.
