That’s because you have installed one of our Block Themes.
Block Themes are a new type of theme introduced with WordPress’s Block Editor capabilities. Unlike traditional themes, Block Themes allow you to customize your entire website layout using blocks, including the header, footer, and sidebars.
You can access these layout options under Appearance > Editor.
This offers more flexibility and design options, but some of the traditional elements, like widgets, are replaced by block equivalents. You can still add similar functionality using block patterns or custom block areas in the theme editor.
Block theme explanation: https://wordpress.com/blog/2024/03/21/wordpress-block-themes/