Hi @daniela_aguado,
In my experience as a Canvas Admin for my institution, I'd say that in my opinion, New Quizzes is a lot stricter in making sure the QTI file adheres exactly to the specifies standards than Classic Quizzes. On one hand, it's good to ensure that files adhere to the standard before importing them, but on the other hand it's not a good experience for users when something imports into Classic Quizzes fine but errors out in New Quizzes.
Ultimately, it seems like it's up to the creator of the QTI file to ensure it adheres strictly to the standard, and does not mix and match versions of the standard inside it (something I've seen happen with files form multiple different vendors). I'm very leery about using ChatGPT or other GenAI services for a task like this, just because they do not generally operate with a strict level of adherence to standards. You might get something to work, but I don't know that it would work reliable and repeatably.
I hope this info helps, even though it might not be a simple solution.
-Chris