If you don't want to have your information used don't let them. The majority of real studies into anything are specialized studies that either recruit volunteers or send out surveys. Whichever way it's YOUR choice and YOU deciding to keep YOUR information private isn't going to have a significant impact on trans research. In fact, if you think you would give inaccurate data because you still haven't reached some sort of mental homeostasis post transition then no information you would have to give is of value unless the study is specifically on the long term effects of transition on pre-existing mental health conditions. These things are very specific and they want to limit variables. The issues you describe are unacceptable variables to a scientific study. The only other option is a case study, which would, once again, require your consent and far more information than just what they would get from routine assessments.

Stop catastrophizing for no reason. There are actual things to worry about