Myer-Briggs tests are a grift, yes. Autism testing is nothing like that. It is assessed by a professional and partly through questionnaires.
Autism itself is not "treatable", so you get no pills or anything. Some symptoms of autism that you may struggle with may be alleviated with treatment, but it's almost all learning techniques and management.
A diagnosis at your age may make it easier to understand, accept and manage some aspects of yourself. For some, that is useful, for others not.