This page here (Jetson Orin NX Series — Jetson Linux Developer Guide documentation) says that PCIe C9 is “PCIE x1 (C9), RP”.
On the other hand the v1.0 Design Guide on page #43 says: “PCIe Interface 3 (x1 – Controller #9. Available if PCIe IF #2 is used as x1 only. Supports Endpoint only)”
The v0.6 Orin NX data sheet says that the x1 ports are Root Port only, so presumably the DG is incorrect and has a typo?