The solver often issues this warning. I see it when the structure has exactly the correct connection to ground to prevent rigid body motion so it should not issue that warning, but since I know the constraints are correct, I can ignore the warning. In your case, rotation about the revolute axis is free so the warning is issued. But you know that the contact at the teeth are going to support that rotation so you can ignore the warning.
Thank you for labeling the ANSYS version with the release number for the attached archive. That lets me know to start that version to open the archive and send it back to you in the same version! Since I only have the Academic license for 2020 R2, I can't solve your model.
I don't know if the model converges and you are just asking about the warning, or there is still an issue.
I did notice two things that you may want to change. I see you have a 20 degree rotation that ramps from 0 to 20 over Step 1, which is fine, but you also have a Moment that ramps from 0 to 1 N-m over the time step. I suggest that what you may prefer is to change this to a 2-step simulation. In Step 1, hold the rotation at 0 degrees while the Moment ramps up to 1 N-m, then in Step 2, rotate the other joint while holding the Moment constant at 1 N-m. The other change is to use the Direct solver instead of the Iterative solver.