Learned the hard way that you can often get the accommodation without the whole conversation. Nobody needs your diagnosis to hear "I do my best work with written instructions — can we do this over email?" or "I concentrate better with headphones; flag me on chat and I'll respond fast."
Frame it as how you work best, not as a medical request, and most reasonable managers just… say yes. Save the formal disclosure route for when the informal one fails — you can always escalate, you can't un-disclose.