I was diagnosed when I was 6 and for me it was necessary back then because I needed support and assistance from teachers. As an adult, diagnosis only really serves to confirm your suspicions but doesn’t really “help” you in most adult situations. If you believe you’re autistic, and advice and helpful systems for autistic people also help you, then who cares if it’s diagnosed or not?
Yes, some weird people online might gatekeep for some unknown reason but its not like having autism is some special elite club or anything. The only thing I don’t like personally as an autistic individual is when other people with “high-functioning” autism (diagnosed or not) use their neurodivergence as an excuse to not be held responsible for their behavior in the slightest.
Like this one dude in my class was extremely rude and sexist and when someone confronted him about it he said they were attacking him because he’s autistic. Like brother no, we don’t care about that, you’re just an asshole. Or this one girl I worked with who would claim she can’t do all sorts of simple tasks because she’s autistic and would get overwhelmed, but she was a full blown adult and perfectly capable of sweeping the floor or moving some boxes.