However to counter this, it's proven that you can't force change your sexuality (it can naturally shift over the course of a person's life, which is very different) so wouldn't adult conversion therapy technically fall foul of misleading/false advertising laws?
Sexual orientation is a Freudian psychological concept that was made up in the 1890s. That the current liberal gospel requires a relatively new theoretical invention be regarded as an immutable human characteristic is as uninformed and uncritical as it is radical. If you reject or critique this orthodoxy, then you are invariably labeled a bigot or homophobe.
If, like you say, your sexual orientation can naturally evolve or change over the course of your lifetime (presumably from changes in brain physiology) then there is no reason these same changes can't be induced as a result of drugs or other interventions (i.e., conversion therapy.) In fact, it is the insistence on sexual orientation as the modality of human sexual expression that even makes conversion therapy theoretically possible.
You are so good at using big words while saying absolutely nothing.