^ Re: nested sections; I know it is not a native solution but HappyAddons does have unlimited sections nesting. See:
https://demo.happyaddons.com/unlimited-section-nesting/
As for sidebars, Elementor offers the following help:
How do I add the Widgets menu option?
To enable the Widgets menu item in the WordPress admin menu, use the following code:
if (function_exists("register_sidebar")) {
register_sidebar();
}
You can add this code to your
child theme’s functions.php file. Alternatively, you can use a 3rd-party plugin such as
Code Snippets to add functions to your theme without needing to use a child theme, and without needing to edit the functions.php file.
Once you have the Widgets menu available to you, you can assign Widgets to the Sidebar as usual in
Appearance > Widgets. You can then use this Sidebar anywhere on your Elementor page. Simply add a column in a section and drag the
Sidebar widget into the column.
If you prefer to register new or custom widget areas via code, instead of using the Sidebar widget (for example, if you need a sidebar on a non-Elementor page), you can find sample code in the official WordPress
Widgetizing Themes documentation. Your code may differ from the sample code based upon your particular needs.