Guest access and Feedback functionality is very misleading for Teachers.
The documentation is clear in that Guests can only use Feedback successfully on the front page of the Moodle yet, when Guests log in and access a Feedback within a course, by default, Moodle allows the Guest to click on the preview icon, fill out the form and click Continue. The Guest doesn't necessarily know this is only a preview and that the results will not be saved. There is no error or warning message and it appears to let the Guest complete the Feedback which is misleading to the Guest and the Teacher administering the site.
I have found a way to get around this by modifying the Guest role so they are not able to view Feedbacks but my question is why would a guest even be allowed to access/preview a Feedback in a course if the functionality is disabled here? What purpose does this serve if they cannot save results? If there is a use-case for this, It might be useful to implement a warning at the very least so that guests are aware they are only previewing the Feedback and not actually completing the feedback.