How to use Checkboxes and Radio Buttons on Field Widgets in Drupal
If you create an entity reference or list field, you will notice the “Check boxes/radio buttons” widget on the “Manage form display” page. How do you switch between checkboxes or radio buttons? Because the widget has no settings to choose the form element.
Drupal automatically switches between the elements depending on the “Number of values” option on the “Field settings” page.