when your head move, and with it your eyes, you move what's in front of them to your perspective inside the simulation, just as VR works

but in this case it is detrimental because the screen is fixed, the natural behavior would be not to move it

or at least do very little with it like a parallax

the current demo would cause nausea after a moment

This is a good example of having sound logic but not understanding the actual use case. It's simply a way to add functionality in a way to attempt to mimic what humans are capable of in a game. Not everyone wants to or is capable of using VR for various reasons. This allows you to use a slight physical movement of your head to replace using a mouse to move the camera, primarily in flight and racing simulators. That means you don't have to take your hand off of the racing wheel to move a mouse around, or even need to have a mouse available to you.

People playing simulators such as DCS are used to have head tracking with OpenTrack. It's very helpful

Have you tried it or is that your theory?

Don't all headtrackers work like this? Also the infrared ones.

Tons of people use head tracking like this via TrackIR and similar setups, it's quite common for space or air sim games.

When I used a head tracker (homemade infrared one), I just got used to shifting my head but keeping my eyes on the screen. Having a wider screen helps.

This is underrated advice. Wish someone told me this 5 years ago.