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.
I try to use the "copy to..." feature to copy a quiz within my course, but my course is not given as an option, only other courses. I'm unsure what I'm doing wrong!
Do Not use Copy To. Copy to creates additional bookmarks but not a unique quiz. If you open the original quiz and then open the copy, you will see that they have identical quiz ids in the URL. Editing one version edits the other and you will not have 2 unique quizzes. Copy to should only be used to copy to a different course.