What is the temperature when the ends are Fixed? In my model, the ends are Fixed at 20 C.  Then I apply a Thermal Condition of 120 C and stress builds up as the part expands. The Enironment Temperature is the temperature when the part is stress free. The Thermal Condition changes the temperature from the Environment Temperature to another temperature.

In your case, the ends are fixed at 120 C and you are cooling the item down and it contracts.

It is simpler to see a purely axial stress in the part if you use displacements to fix the ends but leave the radial direction free.  Create a Cylindrical Coordinate System on the flat circular end face. Delete the Fixed Supports. On one end face apply a Displacement, use the Cylindrical Coordinate System and Set Y and Z to 0 but leave X Free. On the opposite end face, apply a Displacement, but set only Z to 0.  Plot the Normal Stress in the Z axis and you will see a uniform axial stress.