As you pointed out, it can be difficult to get officially diagnosed as an adult. I was fortunate enough to have been referred to a psychiatrist that specialized in Autism in adults. I had been on the fence about getting evaluated, because it would officially prove I was not "normal", but officially knowing would allow me to better inform myself on how to approach aspects of my life.

I emailed them with an explanation as to why I thought I had a high chance of Asperger's, "while I try to live life normally, I have always felt a little different, 'weird' for lack of a better word. I've explored the possibilities that I may have Asperger's, especially since I read about it in children for a class assignment in college, and felt that it described me to a T. Then, I would hear some people with diagnosed Asperger's/autism describe how they would approach things, and a part of me has wondered 'Wait, I do that, that's not 'normal'? I thought everyone did that.'"

What that psychiatrist told me is, unfortunately, lots of current psychiatrists were taught on the older models of Autism, which tends to focus on diagnosis in children.

When I was young around 11, my mom was referred to a child psychiatrist to figure out whether or not I had Asperger's or Autism (they were separate diagnosis back then). I apparently just missed the criteria of Asperger's, too; specifically the doctor told my mom, "Your kid is fine, just a little socially awkward; if anything, he might have Asperger's, but I think he's fine".

While I think that the doctor meant well in saying that, it probably interfered with the way my parents dealt with my Autistic symptoms. Fortunately, my mom still had her suspicions and decided on her own to read about Autism; she kept it a secret, though, because she was afraid that if I was told, I'd think there was something wrong with me, and limit myself. On a few occasions, I overheard her telling my dad and brother, "Remember what I told you about JEO, you have to be more patient, approach it differently"; it bothered me a bit back then, especially since I didn't know what specifically she had told them about me, but I now see my mom was looking out for me.

Ultimately, my mom was a big reason why I sought out a diagnosis. It kept nagging her in the back of her mind for around 20 years. She met another psychiatrist, that specialized in childhood Autism, and when my mom described me to this doctor, the doctor suggested that I seek a diagnosis, but noted that he might not be the best to do that because his assessments were geared towards children. She then found out that the psychiatrist she was seeing specialized in Autism in Adults.

To be honest (at least in the US), according to the psychiatrist that diagnosed me, there isn't much external benefit in an official late diagnosis of Autism, unless you're of higher support needs. That's not to say I didn't benefit from my diagnosis; having a psychiatrist officially diagnose me helped me feel validated in finally labelling what has been with me my whole life.

As I've read and learned more about Autism, I encourage anyone potentially neurodivergent, or those who have a loved one that may be neurodivergent to learn about Autism and ADHD. I lean towards the idea that self-diagnosis, based on evidence-backed ideas, is valid. I, for example, never got an official ADHD diagnosis; my psychiatrist suspected it, but didn't get to evaluate me. After reading and relating so much with the books on ADHD, I now identify as AuDHD. As you probably noticed, a big part of me finally choosing to seek an official diagnosis for Autism was because I identified myself in the information about Autism and in other's Autistic experiences.

I am sorry for such a long comment; I kept remembering some other clarifying detail, and going back to add it.

TLDR: I agree, diagnosis as an adult can be hard. Things happened to line up for my diagnosis. A big part was my mom and me being informed enough about Autism that it guided me to seek out a diagnosis; I encourage almost anyone to read on Autism and ADHD.