Please don't continue to share this "fact." I know it sounds like a really good gotcha, but it's not. Tylenol is just a brand name producer of the drug acetominophen, known in most of the rest of the world as paracetomol. It's been around since at least 1878, and possibly earlier (there are claims it was produced in 1852). Autism was first described by Leo Kanner in 1943. Obviously, anyone sane knows that it's been around a lot longer than that, probably as long as humans have been humans, but the people you're trying to reach with this claim are obviously going to assert that it first appeared around the same time that it was first identified, or, at the very least, that it's appearance likely aligns with the invention of paracetomol.

Adding to that what @Voroxpete@sh.itjust.works said: “links to” doesn’t mean “is exclusively caused by”.

That gotcha would only work if that was the claim.

So the argument reads a little like “People died before the Ford Model T entered the market, so obviously deaths aren’t caused by cars running over pedestrians.”