Science

Plenty of historical figures had what we now recognize as different forms of neurodivergence.

Peter Roget obsessively made lists throughout his life, beginning as early as 8 years old. He also liked to solve chess puzzles and invented the log log slide rule, useful for working out exponents and roots by hand. He appears to have suffered from depression, and used list creation as a mechanism for calming himself. After he retired, he catalogued lists of synonyms and compiled it into categories, creating what would eventually be known as Roget's Thesaurus. Looking over his biography, it's pretty obvious that he would be considered neurodivergent today.

Sherlock Holmes had trademark characteristics of what we would later call Asperger's: obsessive attention to detail combined with disinterest in other humans or their emotions. He's a fictional character, but his creator, Sir Arthur Conan Doyle, almost certainly drew on his own life and a few others in his life to create that character.

But we document these historical figures through writing, so anything prehistoric would likely not show up in the same way.

A disorder also doesn't really "exist" if it's not actually causing distress or... well, disorder. Mental disorders are basically cultural constructs in that what is disruptive in one culture isn't necessarily disruptive in another. "ADHD" in one culture may be "wow, she's really good at hunting" in another. A schizophrenic person in one culture may be a cleric in another.

Or there were very different ways of interpreting and managing them.

I was referring to currently existing ones.