To create pages with 'full width' as default, they'll need to be 'database pages'. So, we'll need to create a database.

Click "Press Enter to continue with an empty page, or pick a template (↑↓ to select)"

Press Enter to continue with an empty page, or pick a template (↑↓ to select)

Click "Add a new inline database to this page."

Give your template page an icon if you like.

And voila! You can now create full width pages with a click.

You can also set the default 'open' view to be full page.

And you can also set your database to create the full width page template by default :)

Now just create new pages within the database and you have a full width page with one click!

Full Width Notion Default Pages