Um, I believe in philosophy, this is called a non sequitur, meaning you've made a jump in your argument that is illogical. Just because someone who is not a scientist (e.g. Greta) advocates a valid scientific proposition (e.g. climate change), does not mean the valid science is invalid because of the person advocating it - or the person who advocates on behalf of the advocate is not a scientist. For example, if someone, who is say mentally challenged, said that the acceleration due to gravity is 9.8 metres per second per second, you could question the intelligence of the person who quoted the formula, but to question the validity of the fact itself is not logical.
And whether she is autistic or goes to school has very little to do with intelligence. Here's shortlist of high school dropouts:
Albert Einstein
Arnold Schwarzenegger
Richard Branson
Quentin Tarantino
George Carlin
Charles Dickens
Ray Kroc
John D Rockerfeller
Benjamin Franklin
Jay Z
Marlon Brando
John Travolta
Frank Sinatra
David Bowie
Prince
Curt Cobain
Walt Disney
Being a high-school dropout certainly does not mean you will be accomplished, but neither does being a high-school dropout mean that one is unintelligent. Another non-sequiter in your argument.
And while we're on the topic, here is a list of folks who are autistic or on the spectrum:
Charles Darwin
Albert Einstein
Bobby Fischer
Bill Gates
Thomas Jefferson
Steve Jobs
Alfred Kinsey
Nikola Tesla
Sir Isaac Newton
Andy Warhol
James Joyce
Again, being autistic does not preclude intelligence. In fact, as you can see, some of the most accomplished people in history were on the spectrum. In fact you could say it is an ingredient in very advanced intelligence.
And finally, I will point out that you committed one of the basest logical fallacies in disparaging Ms Thunberg: an ad hominem argument. That is, in the absence of a logical argument, you resort to insulting someone's character. Kind of lie telling someone she can't be right because she's a woman, or a ni**er, or a ch**k, or a p*ki.