Employers and schools often google the names of applicants.
If googling your name turns up a reference to you being autistic on the first couple of pages, then some schools and employers will find out that you are autistic.
And whatever prejudices they have about autism will affect your chances of being selected.
One example is: If you talk about being autistic in the school paper, that will likely make that information show up on Google where prospective employers can see it.
That doesn’t mean being open about autism is necessarily a mistake. There are major advantages to being open about it. The point is that it’s worth paying attention to how open you’re being (which might be more open than you think), and take the risk into account.