Setting Global Defaults
Global Layouts are used as a fallback for all the allowed post types if a specific layout for that post type or post is not set.
The Global Area Layouts tab on the options page displays a list of all the areas registered on the site. For each area, you can define a fallback layout that will be used if no other layouts exist. These layouts need to be created with the new (since 1.6) Layout Builder. Any saved layout that has been created with the Layout Builder (and is allowable in the selected area) will show up in the dropdown as a default area layout option.