From responsive 4.0, the HTML structure has been changed to comply to latest W3C standards and for compatibility with Gutenberg.
Layout - New Layout Options - Old layout options in Customizer has been consolidated.
The following have been removed:
Default -> Move to Boxed
Full Width Layout -> Move to Full Width / Content
Full Width No box -> Move to Full Width / Stretched
Now you have to use new layout options to your website based on your requirement as below
Boxed (This will be the new default)
Full Width / Content
Full Width / Stretched
You can find these option in the Customizer setting -
Also you have able to change the individual layouts of the page/blog page/blog entry page
If using you were using Full Width No boxed layout then use the site layout as Full Width / Stretched Layout
For child themes or custom-css: div id=content-outer has been changed to class outer-content, this was done for W3C compatibility. Please use class .content-outer in your custom css.
Primary and Secondary Id for the content and sidebar.
For sidebar white color is used as default background color. You can change sidebar color from Customizer > Appearance > Sidebar > Sidebar Background Color.
Menus (Sub header menus and the top menu have been removed):
We have removed the sub header menu and top menu to reduce the complexity.
Now you have only Header menu option and you can place it where you want like about the header or below the header.
Top menu has been removed and replaced by widget area:
If you want to use top header menu for your website, use header widgets area and add a menu in this.
The following change is done to Header layout & Menu position:
Default -> Menu position will be Below header & header layout will be Logo left.
Footer Widgets: Footer layout option has been replaced by Footer Widgets Layout in Appearance -> Customize -> Footer and now you can select upto 4 columns for footer widgets.
Please go to the settings and update Footer Widgets Column and then select widgets for different columns in Appearance -> Customize -> Widgets