I hope this is fake. You cannot simply call something a mental illness because you disagree with it. The five principles of defining a psychological disorder prevent this so hopefully it wouldn't be a thing diagnosed by actual mental health professionals, although most of them do seem to be liberals. They probably wouldn't have an issue with ignoring the 5 principles if it aligned with their beliefs.

One of the principles this would violate is that it cannot be a conflict between an individual and society. Another is that it must cause significant distress in a person to the point it affects his or her daily life such as work or school. These two alone would invalidate "misgendering" someone as a mental disorder.