// Disable Gutenberg (Block Editor) for all post types and posts
add_filter('use_block_editor_for_post', '__return_false', 10);
add_filter('use_block_editor_for_post_type', '__return_false', 10);

// Disable the default block editor for widgets
add_filter('use_block_editor_for_widgets', '__return_false', 10);

// Disable the block editor in the admin area for posts and pages
add_filter('current_screen', function($screen) {
    if ($screen->base === 'post') {
        remove_action('edit_form_after_title', 'wp_richedit_pre', 10);
    }
});