If you want to select a certain page for something in your WP theming needs, check this out:
How to Add Dropdown or Select Pages in WordPress Customizer
General solution for drop-down select menus:
https://wordpress.stackexchange.com/questions/270070/add-a-dropdown-to-theme-customizer
That works, but I think radio button is underrated and poorly documented
Enter the destination URL
Or link to existing content
