I'm neurodivergent myself (ADHD), and I often ask myself how my particular brand of divergence would be modeled by D&D rules. Here's my advice and suggestions, for what they're worth.
Whatever you do, resist the urge to make this a "racial" or cultural thing. Being autistic isn't a "subrace" or a "profession," and implications to the contrary will always be offensive. However you choose to address the topic, it must span all cultures, races, and backgrounds.
Also resist the urge to write new rules. The existing rules are plenty to build any kind of character upon--including neurodivergent ones:
- Many of the feats in 5E can be excellent stand-ins for particular types of neurodivergence. If you rewrite the flavor text a bit, the Alert and Prodigy feats can describe the insomnia, anxiety, and hyper-focus of being attention-deficit. Keen Mind could be reskinned to describe someone with a photographic memory, Observant could describe someone with heightened awareness or anxiety. I'm sure there are more.
- The Personality Traits, Ideals, Bonds, and Flaws presented with the character backgrounds are just suggestions, you should feel free to write your own to describe how your character views and reacts to the world at large. Work with your DM and fellow players, and tread carefully when you get to Flaws.
- Your choice of proficiencies and skills could reflect your character's habits and mannerisms. Your character might have very different reasons for learning how to deceive others, learning how to be unseen, or learning how to play a musical instrument. Choose the skills, tools, and languages that best describe your character, not necessarily the ones that give you the best stats. (This is good advice for all characters, actually.)
That's all I can think of off the top of my head. The goal is to play the character you want to play, without being disrespectful of yourself and your fellow players. If you do that, everything else will fall into place.