What does this specific law cover? I could see how adult "conversion therapy" bans could theoretically violate the First Amendment. If this is a law designed to protect minors, I think that's another issue entirely.
Yes if an adult wants to try to change their sexuality (causing themselves mental trauma and wasting a lot of their own money in the process) then it is arguable that they should be allowed to do so. 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?
However parents forcing their child to go through it is simply child abuse by another name and there's no question that it should be banned. I really hope that this is not what is upheld in the end...