I don't know whether this suits your purposes but I was just trying to figure out a similar challenge (how to allow public viewing of quiz content) and found that ungraded quizzes can be taken without a user account and will automatically mark multiple choice type questions (any questions that can be auto-graded). It just won't retain any scores since there is no account associated with the quiz taker.
I want to add something to @sys_lam's excellent answer. If someone is logged into the Canvas instance and views an ungraded quiz or survey in a publicly visible course in which they are not enrolled, they can't take it. However if they log out of Canvas, they can. There is a difference between institutional and public users as well as visibility of courses in this respect.
It doesn't make sense to me that it works this way, but that's why my testing confirms.