We understand that you are trying to convert New Quizzes to Classic Quizzes and having to do so manually. We understand that it is time consuming to copy and paste questions one by one. Currently, we do not have any easy procedure to convert New Quizzes to Classic, but can easily convert Classic to New by using the "migrate" process.
Ideally, we want to have one comprehensive quiz tool for everyone to use without any discrepancy between versions and setups. Because we are working on getting New Quizzes fully integrated with all the pros of Classic Quizzes, this feature is not currently being worked on retroactively to migrate New back towards Classic. We are focused to create one fully integrated quiz system that takes the best of both options. For the time being, if you prefer to use Classic but only have access to the quizzes in New form, you would need to make the transition manually the way you've been doing it. We know this isn't ideal, and we appreciate your patience while we work to make the Quiz Feature in Canvas intuitive and easy for all.
Should you need to convert it the way we currently have it set up, here is the guide: