Starting from WordPress 5.8, the block editor includes a new Widget Blocks feature that replaces the traditional (“classic”) widgets screen with a block-based interface. If you prefer to use the classic widgets interface, you can disable the Widget Blocks feature using the following code snippet:
add_filter( 'use_widgets_block_editor', '__return_false' );Note that this method is only a temporary workaround and may not be supported in future versions of WordPress. It is recommended to familiarise yourself with the new block-based interface and migrate your widgets to the new interface if possible.