I ended up with like half an autism diagnosis a bit over ten years ago. (Basically, I saw someone for other reasons and they said “Um… I’m pretty sure you’re autistic, you should go talk to these people for a proper diagnosis” and I never did.) Occasionally the idea resurfaces (and is again at the moment, to some degree, because I’m having problems at work that are surely neurodivergence related) and I end up dropping it. Mostly, as far as I can tell, as an adult who is able to live independently, maintain employment, and isn’t going to return to education, there really aren’t many/any resources out there, so it feels a bit pointless. Some people do get a lot of benefit from the confirmation/certainty that comes with a diagnosis, so you may feel a diagnosis is worthwhile for you, even if it doesn’t get you access to any concrete resources. I can’t decide if I’m one of those people or not, to be honest.
Now, there are concrete downsides to diagnosis–some countries will use an autism diagnosis as grounds to deny a visa; in the US it’s not an unrealistic worry that it’ll make accessing medical transition harder if you’re trans; I have a friend who has come down on the side of “no official diagnosis” for fear it could jeopardise his access to ADHD meds in the future. (I picked up an ADHD diagnosis a couple years ago – I’d been taking meds for anxiety and switch psychiatrists and they were like “Umm… I’m not saying your not anxious, but you’re actually describing ADHD”. I suspect my brain lies in the autism/ADHD uncanny valley. I mention this as a lead in to say that I don’t share my friend’s fear, but it’s also not an unrealistic fear.)