DEFECT: unchecked Can Request Events - Calendar Request Events button usable
There seems to be No direct fix right now regarding the situation that Unchecked "Can Request Events" does not full prevent the Calendar page Event Request button from being visible and useable.
It seems that Guest Roles also need to have a specifically define default calendar along with unchecking the "Can Request Event" permission in order for that button not to show on the Calendar page.
I demonstrated in screen snippets and writing our steps to reproduce the scenario 3 times for a support case.
So far, the recommendation is a bandage workaround of setting a default calendar for the Roles that your institution does have unintended people submitting Event Requests.
Best regards, Jason Madden