This just hasn't been my experience. I've been through the diagnostic process for all of my family:
DD1:
ASD (15 at diagnosis, but under paediatrician since 2 years 9 months, 1:1 at preschool and special school since 4). Questionnaires to both school and home. School questionnaire completed with great detail (I was given a copy). ADOS completed by a specialist SALT and an Occupational Therapist. Developmental interview by a Consultant child psychiatrist. The report covers early developmental history, medical history, family history, risk, educational history, the ADOS findings, developmental interview findings and the concluding diagnosis.
ADHD: now aged 20. Currently in progress. Consultant learning disabilities psychiatrist is assessing. We've had 2 hours of assessment so far, but due to DD1's difficulty in coping with sessions, it's likely to take a further 4 sessions of assessment before a decision can be made.
DD2:
ASD diagnosis at 11. School and home questionnaires. ADOS face to face, 3Di interview face to face. Again, SALT, OT, Psychiatrist.
ADHD (inattentive) diagnosis at 18. Questionnaires, video assessment with two different clinicians on separate occasions.
DD3:
ASD diagnosis at 15. School and home questionnaires. ADOS online. Developmental interview online.
ADHD assessment at 15 face to face with Consultant child Psychiatrist. QB Check test.
Me:
ASD assessment online with questionnaires and developmental interviews. Needed information back to early childhood. SALT and OT.
ADHD assessment online. Questionnaires for both me and my DH. The assessor wouldn't ask specific questions because he said that he tended to hear 'cookie cutter answers based on TikTok videos', so just introduced themes and asked me to explain why I thought I had symptoms in those areas.
DH:
ASD assessment online. Questionnaires to him and me prior.
ADHD assessment online on 2 separate occasions with 2 different clinicians. Questionnaires to him and me. For the 2nd interview they requested his Mum join to give an early childhood perspective, despite the fact that she now lives in France, because I have only known him since age 19.
I don't doubt that some people convince themselves that they have ASD or ADHD, absorb all the info available on TikTok and then parrot it out at assessment. In fact my ADHD assessor said that he spends much of his day telling people that they don't have ADHD and that what they've seen on TikTok is not hallmark ADHD. They are actually looking for much more subtle signs than 'I get a bit distracted, me' or 'I'm so messy and disorganised, aren't I?'