FSX: Steam Edition is more involved than games that only need a single LookPilot protocol. External head pose goes through SimConnect, which opentrack drives—not a SimConnect option inside LookPilot.
LookPilot: set Protocol to opentrack (UDP into opentrack).
Opentrack and SimConnect: install opentrack from the opentrack releases page, then follow opentrack’s SimConnect protocol documentation for the SimConnect client (SimConnect.msi), choosing Microsoft FSX SimConnect as output, picking the right manifest, starting opentrack, and troubleshooting. For the Steam install layout and where to run the MSI, opentrack also documents this in SimConnect FSX SDK for Steam edition (wiki).
With LookPilot: use OpenTrack setup with LookPilot (LookPilot Protocol opentrack, opentrack Tracker UDP over network). After SimConnect is configured in opentrack, click Start tracking in LookPilot, Start in opentrack, then launch Microsoft Flight Simulator X: Steam Edition from Steam. Fully quit and restart the sim once after the first-time setup if it does not react.
The same overall workflow is described in Beam Eye Tracker’s FSX: Steam Edition guide.
Usually no separate in-game “enable TrackIR” step is required once opentrack’s SimConnect output is working. If the camera still does not move, use Troubleshooting in opentrack’s SimConnect protocol documentation.