Sorry this answer is more slanted to ADHD but hopefully still relevant.
I had a private ADHD diagnosis. This was after years of feeling different, struggling with socialising in groups and deadlines, stress and quitting school/ jobs, feeling extreme exhaustion etc. I kept wondering when I would grow up, i.e. be able to "do all the things" other adults did like work/look after domestic stuff/have a social life without chronic burnout.
I am currently in the middle of an NHS autism assessment after the ADHD-diagnosing psychiatrist said I was presenting with ASD traits as well.
I'm old enough not to have to give a stuff about what employers or other people think or need a visa. But I do get some people's reluctance to get diagnosed in case disclosure to their employer makes life more tricky. Some employers will be helpful, others will not understand at all. I am very open about my diagnosis. I am self-employed and am gradually building sensible boundaries to avoid overwork and trying to communicate such in a positive way to customers and others. People have been largely very very supportive. What I don't do is present myself as a "neurospicy creative" like ADHD is a really fun thing. That annoys me. If ADHD is so positive for you why did you need a diagnosis?
With regards to NHS, I want it firmly on my records because I have always struggled to engage with healthcare and am starting to understand why.
My main problem is family. Few accept that I genuinely have ADHD as I have masked pretty effectively for decades. Again, I am building boundaries to maintain some balance in life but it is a struggle as I am at the life stage of elderly parents needing lots of help. I am happy to help but cannot take the full burden as I know it will just push me to total burnout.
Did I grieve? Not really. I'm angry that women like me have gone unnoticed and undiagnosed for years, yes, but I don't wish away meeting my DH and friends and colleagues that I wouldn't know if my life had taken a different trajectory.
Has ADHD diagnosis solved all my problems? And will an ASD diagnosis do the same? No. But it has helped me understand myself better and where possible organise my life so that I'm less stressed and over-committed.
Will an ADHD or ASD diagnosis help you? I have no idea as everyone is so different in the presentations of ADHD/ASD. My very rough rule of thumb answer to anyone who asks if they should get a diagnosis is this: are the symptoms having a negative effect on a daily basis? If not, then maybe you aren't ADHD or ASD. E.g, misplacing your car keys occasionally is normal, losing stuff multiple times a day isn't.
I would agree that there isn't much support outside meds or hiring a private therapist. (I can't take the meds for other health reasons and not in therapy) I have been offered a coffee group at a local supermarket and a FB group. And maybe NHS CBT if I wanted it. I am told by everyone I know who has tried CBT that it's useless.