How to have a default selected item of Multiple Choice "List of Options"?

In the page type field for Regions under General in the field Default value enter General. If you dont want the user to be able to select it, and want it to always be General then uncheck Display field in the editing form. See Example

If you want to just display the checkbox and disable it to prevent your users/visitors to uncheck it, please create a new "dummy" field just for that text box (boolean) and set Enable condition to false.

I'm assuming your scenario is to have "Default" as the value of the Regions field, if no selection was made in the "multiple choice" selector.

The logical approach would be to set a "Default" value in the configuration of the field, however the "multiple choice" selector will simply overwrite this with a blank value when the data is saved. So this is not an option, unfortunately.

I believe your best bet is to clone the "Multiple choice" form control and add a "default value" setting, or develop your own custom form control