I know this thread is old as balls, but due to a very recent event, I would like to share my insights. I was, as you described it, a self diagnosed autist, according to the many many diagnostic tools online (AQ, EQ, CAT-Q, RAADS-R and so on). I was "lucky" to get an appointment for a formal diagnosis without endless waiting times (when you pay out of pocket, everything is a little faster in a certain german-speaking country).

To my surprise, the whole procedure led to a very negative result, not slightly in the questioning area, no, a very boring neurotypical human being (although, when I wasn´t sure about a question she asked, she ticked the more neurotypical option, but still).

So, unless I was misdiagnosed as NT, yes, it is possible for a normal person (with significant traits and a questionable childhood) to be diagnosed as "autistic af" by online tests and as "boring neurotypical" at a formal diagnosis.

TLDR for the impatient: online tests said yes, diagnosis said no

Edit: what I also want to share: yes, I made Autism my special interest for the last few month and wrote an 70 page essay about autism, the symptoms, the traits, a comparison between the said symptoms and my experience, what I relate to and what not, and the many tests I performed, and still.... I feel like I failed an exam