CSS

wordpress classic editor on post type

add_filter('use_block_editor_for_post_type', 'prefix_disable_gutenberg', 10, 2);
function prefix_disable_gutenberg($current_status, $post_type)
{
    // Use your post type key instead of 'product'
    if ($post_type === 'product') return false;
    return $current_status;
}