I believe the rudder axis has to be the Rz or Z-Axis. Can you ,in the Thrustmaster software,somehow change the Rudder axis from Slider1 to Z or Rz?

Edit: Something more to note,a controller needs atleast a X and Y axis to be seen by the Sim when in the mission. I had a problem too,long time ago,where my Pedals didn't have a X and Y axis. Doesn't matter if the Keymapper sees them without those requirements.