Reformat your example slightly, and suddenly it's not so bad:

  public function html2wikitext(
    PageConfig  $pageConfig, 
    string      $html, 
    array       $options = [],
    ?SelserData $selserData = null
  ): string

I am sure an IDE could do that for you.

That being said, I think the Python way of formatting type annotations ("variable : type") is more readable than C-style "type variable = ...", especially when the annotation is optional.