It only talks about an increase in diagnosed cases

Yes, in the type of autism least likely to be missed previously.

which can be explained away by more frequent assessments, better awareness of symptoms, the loosening of diagnostic criteria in the DSM IV, and over-diagnosis to get children with other severe developmental disorders qualified for services. There are lots of reasons we know about that autism is being diagnosed more frequently, but the best you’re going to get on your hypothesis is “we don’t know.”

Sure, but there's no evidence it isn't also increasing, and plenty of evidence it is.

Environmental risk factors may also play a role, perhaps via complex gene-environment interactions, but no specific exposures with significant population effects are known

This downplays the importance of environmental factors. It's not just a "may also" situation.

• Twin studies: Identical twins have a higher concordance rate for autism than fraternal twins, suggesting a strong genetic component. However, the concordance rate isn't 100%, meaning environmental factors must be involved.
• Increasing prevalence: The rising rates of autism diagnoses cannot be solely explained by genetics. Changes in diagnostic criteria play a role, but environmental factors likely contribute to this trend.
• Specific environmental links: While no single factor has a massive population-level effect, research has identified several environmental factors associated with increased autism risk such as advanced parental age, valproic acid, air pollution and other prenatal exposures. All of which have increased over time. Hence, the rate of autism is increasing, not just our diagnostic ability.

A more accurate statement:

"Environmental factors play a crucial role in the development of autism, often through complex interactions with genetic predispositions. While no single environmental exposure universally causes autism, research has identified several factors that significantly increase risk, including advanced parental age, prenatal exposures to certain medications and infections, and birth complications. Ongoing research continues to uncover the intricate interplay between genes and environment in autism."

https://www.autismspeaks.org/autism-statistics-asd

Autism Speaks is a hate org and should not be referenced.

Now, do you think it's a coincendence so many trans people are autists? Or maybe there is a biological explanation?

Studies have suggested a higher prevalence of non-heterosexual orientations and gender nonconformity in individuals with NCAH, particularly in females. This may be due to the impact of elevated androgens on brain development during critical periods. Mild mutations in CYP21A2 are relatively common, occurring in an estimated 20-30% of the general population. These mutations can lead to subtle variations in hormone levels, even in individuals without a formal NCAH diagnosis. These variations likely contribute to a spectrum of androgen-related traits, including those related to sexual development and behavior.

If it were due to this gene cluster. You would expect to see the disorders it cause cluster in LGBT people (Auotimmune (SLE, RA, MS, T1D, Thyroid), Hypermobility, Schizophrenia/Autism/ADHD, CFS, MCAS, POTS).

And for people to start noticing with threads like this;

https://old.reddit.com/r/DrWillPowers/comments/wybnef/the_nonad_of_trans_i_continue_to_see_more/