Ah, fresh new research. An interesting one. https://link.springer.com/content/pdf/10.1007/s00406-020-01189-w.pdf about misdiagnosis of autistic adults. Sample of people diagnosed as adults:
161 adults, 47 of them female. Females diagnosed avg age 26, males at 22.
Only 26 had an intellectual disability. Shockingly/

...it took an average of 11 years for the diagnostic teams to diagnose autism.
In the meantime, a third were given a diagnosis of something else. A quarter were given 2-3 diagnoses of something else. Nearly 1 in 10 was given 4-5 diagnosis of other things/

The previous gambits at a diagnosis include schizophrenia, personality disorders, and OCD. The paper outlines some of the diagnostic clues that would have guided the teams to the correct diagnosis (though some of course may indeed have more than one thing).
Couple of errors/

No, females do not "...present more frequently uncontrollable mood and interpersonal problems". The research quoted was from 10+ years ago, when we had found very few of the autistic females. More are being diagnosed. Originally, dx was for most 'extreme' situations, and/

...the first old study was of only 20 autistic females, the second was not a study of autism but of BPD, and only found 6 autistic females in total. It's never appropriate to make pronouncements about all autistic females based on old & tiny samples like this.

So, in summary, it's an average 11 year journey to get a diagnosis that only takes a few hours. And in the meantime, so many are given incorrect labels (as well as some that may be correct...but autism is missed every time...). How many end up on drugs they never needed?/

How many end up with severe mental health difficulties because of that diagnostic delay, too? Left unsupported.
How many end up with society thinking they're 'more unstable', based on sloppy research, tiny samples and studies that weren't even on autism?/

It is good to see the Psychiatric journals doing some new thinking about all of this. I have no doubt whatsoever that they all want to get this right.
It will be very helpful when they engage further with the autistic researchers, to avoid errors.

Some say, "How dare people self-identify as autistic! Why don't they just trot down to the docs and get that diagnosis!"
Well, my friends, this is part of why. 11 year journey. Endless mistakes on the way for some. It may be perilous.
Society isn't kind, at the end of it all/

After those 11 exhausting years, some can only look forward to a battle for non-existent services, outdated information, a barrage of negative assumptions, and some outright prejudice dumped on top.
It's hardly an incentive, is it.
We must do so much better than this, between us/

For me, diagnosis was a relief. It enabled me to find my peers, to find my own network of support, to be thoughtful about my boundaries and needs.
And to work hard towards changing that awful narrative around autism. e.g. https://annsautism.blogspot.com/2019/01/autism-some-vital-research-links.html

The fabulous autistic people around us are very much in need of more people questioning the old nonsense. Getting to know us.
Working with us as equals.
Realising we never were a 'bad behaviour' or an 'instability'. And cherishing what each of us bring to the world.

I'll add something controversial (and wait for a Psychiatrist to pop up, aghast). It's not that difficult to diagnose autism.
We've made it into a 'three-ring circus' for young people, involving years of teams, analysis & heaven knows what else. What on earth for?/

a) Do they use an autistic social communication system?
b) Do they have extreme focus on their passionate interests, with extraordinary dedication?
c) Do they thrive on routine & predictability?
d) Do some nonautistic people cause them endless difficulties?/

e) Do they have sensory differences of some kind e.g.
Sight
Hearing
Smell
Taste
Touch/texture
Pain responses
Knowing if they are hot/cold/tired/hungry/thirsty
Have they always been like this?

These are basic things, not rocket science.

I train diagnostic professionals to diagnose autism. I am not a diagnostic professional myself and I do not diagnose autism, being clear.
But there sure as heck is no reason for this to take 11 years, is there.

Because I'm sometimes used as a 'test subject' by enthusiastic researchers, I've had some hilarious diagnostic interviews involving farm animals, a house, a car, crayons and heaven only knows what else. Tremendous fun. And nothing to do with autism.

Those related to the old myths about us lacking imagination and having no ability to play in imaginative ways with objects, or explain to others what we're doing.
This might describe a small subset of autistic people.
It's not true for most autistic people.