Is a mature child obligated to obey his parents in undergoing a medical evaluation and psychological treatment, especially since the parents believe that non-compliance will harm the child, while the child believes that the treatment will harm him and does not believe in its necessity?

Apparently, it is obligatory for the child to obey their parents by presenting themselves to doctors and following the prescribed treatment regimen, even if they do not see a need for it or are bothered by disclosing their condition. The potential hardship does not preclude obedience in what is righteous, as long as there is benefit for the parents and no harm to the child, as mentioned by Ibn Taymiyyah.