Searched & tried a lot: Is it Possible to Eliminate Render Blocking Manually

If you want to defer loading of css, see CSS delivery optimization: How to defer css loading?.

If you want to defer loading of js, you can use this:

add_filter( 'script_loader_tag', function( $tag, $handle ) {
  return str_replace( "<script type="text/javascript"", 
    "<script type="text/javascript" defer="defer"", $tag );
}, 10, 2 );