I was using Tobii frequently with MSFS 2020 and with my old PC. Now I switched to a new PC and reinstalled everything. Including Tobii - calibrated and everything ready.
In the MSFS 2020 settings the headtracking toggle is “/” within the numpad - which is what I had with the old PC.
Now, on the new PC when I hit / it would not start tobii. But the sim “sees” tobii as in the control settings tobii is present.