// Disable wordpress editor - gutenberg on Post type post 
add_filter('use_block_editor_for_post_type', 'disable_gutenberg', 10, 2);
function disable_gutenberg($current_status, $post_type)
{
    // Use your post type key instead of 'product'
    if ($post_type === 'post') return false;
    return $current_status;
}