If you did not like Cursed Child and you are struggling with accepting it as canon, this may help you. A short thread

Besides the seven novels, there are three companion books written by Rowling: Quidditch through the ages, Fantastic Beasts and Tales of Beedle the Bard. They have something in common: they are part of the Wizarding World - they were read by the characters we like.

What if we take Cursed Child as a book / stage play that is part of the Wizarding World? It would still be canon - but in a different way. Imagine that it was a book / stage play written by, I don't know, Rita Skeeter? It is based on what Skeeter knows about Harry Potter.

And also about her knowledge on Magical Artifacts. She doesn't know how Time-Turners work so she invented that. After all, it's all fiction! If you like this theory, you can fill the gaps too: It was premiered in a little theater at Hogsmeade.

And maybe, Harry saw it with his family and he did not like how he was portrayed. Of course, Rita Skeeter (or her alter ego, Thorne) got inspiration from real stuff: The rumours about Draco's son being Voldemort's were real, and that's what Rita used it for her book: Cursed Child

This theory would accept Cursed Child as canon and wouldn't contradict the books so much, in fact, it'd add some depth. Take it or leave it, it is just a theory. But if it helps you, you are welcome!