I would rather that the product that I pay for, make things easy for me. I would understand lack of support if I was doing something esoteric or obscure. Duplicating a quiz does not seem to fall in that category considering the target audience of Canvas.
You can also just click on the three buttons form the "quiz" view, choose "Copy to.." and then copy to the course you're in and refresh the page
I made several copies of a quiz using the "Copy To" option and merrily edited each of them as desired. In the end, I found that all the quizzes had been set to be the same as the most recently edited copy.