There are plenty of psychologists that have stated he is a narcissist, specifically, a malignant narcissist. That a particular poster does not have a psychology degree has nothing to do with Trump's narcissism.
What is troubling are the lengths people go to in excusing his behavior.
From
Malignant Narcissism: Does the President Really Have It?
"
John Gartner, Ph.D., is a psychologist who taught at Johns Hopkins University Medical School for 28 years. He says yes, the president has malignant narcissism, as follows in his chapter in the book
Rocket Man: Nuclear Madness and the Mind of Donald Trump (2018):
“Trump suffers from malignant narcissism, a diagnosis [that is] far more toxic and dangerous than mere
narcissistic personality disorder because it combines narcissism with three other severely pathological components:
paranoia,
sociopathy, and sadism. When combined, this perfect storm of psychopathology defines the ‘quintessence of evil,’ according to Fromm,
the closest thing psychiatry has to describing a true human monster.”"