the Customizer > Layout > Sidebar options set the Global rules for sidebar display.
But they can also be enabled disabled in the Post Editor using the Layout Meta box:
I just inspected a single post page, it seems you built it with Elementor.
The whole structure has been replaced by the Elementor template, so there will NOT be any default sidebar/header/footer appears, and GP customizer won’t be able to control any of its layouts.
I would recommend reaching out to Elementor to see if there’s any setting that allows you to use the default WP sidebar.