Post times you refused to acknowledge something as canon

>because of how much of the canon it breaks and retcons
That has nothing whatsoever to do with whether something is canon or not. Inconsistent canon is common. As the prime example, the Biblical canon contains two contradicting stories of creation right after each other in Genesis, and there are four Gospels that don't entirely agree with each other. The Bible wasn't written as a history book, and most works of fiction are made to make money, not to please autists like us. Whether something is canonical or not depends on whether the person or organization in charge of a work says it is. For some reason, Harry Potter and the Cursed Child has been marketed as an official installment in the Harry Potter story, so that's that unless Rowling changes her mind.

>I don't know what a Gary Stu is

We know