Radio buttons should come by pair at the minimum (when dragging a radio to a form).
And they should have an option for one to be checked on by default.
The logic is when you're using a radio button group, answering it isn't optional. (ie: book for monday OR tuesday)
If it's optional, then the whole group should be optional and activated by a checkbox.
Thanks for listening!
Following on this discussion: https://forum.webflow.com/t/radio-button-forgetabout-it/37746/3
And about readings such as https://www.nngroup.com/articles/radio-buttons-default-selection/