I have some forms on my site that I hide categories in this way. I use the following Javascript to hide specific options, including the "friends," "me only," etc.

  <script language="javascript">


const aVars = ['GROUPS'];
aVars.forEach(reduce_vars);
function reduce_vars (sItem)
{
$(".sys-privacy-group").children().remove('optgroup[label=' + sItem + ']');
}  
    
    
  $(".sys-privacy-group option[value=2]").remove();
  
  $(".sys-privacy-group option[value=3]").remove();
    
  $(".sys-privacy-group option[value=5]").remove();
    
  $(".sys-privacy-group option[value=6]").remove();
    
  $(".sys-privacy-group option[value=7]").remove();
    
  $(".sys-privacy-group option[value=8]").remove();
  
  $(".sys-privacy-group option[value=9]").remove();
  
  $(".sys-privacy-group option[value=c]").remove();
  
  $(".sys-privacy-group option[value=s]").remove();


</script>

That kind of what you are looking for?