Make the 2nd column sticky only on Portfolio Pages

you are talking about the news sites?

but if there are additonal columns below – what should happen?

have a look to one of your news pages or the blog page itself:

.responsive body#top.blog,
.responsive body#top.wp-singular {
  overflow-x: visible !important;
}

.responsive body#top.blog #wrap_all ,
#top.wp-singular #wrap_all{
  overflow: visible !important;
}

@media only screen and (min-width: 767px){  
  .responsive body#top.blog .sidebar_right .container,
  #top.wp-singular .sidebar_right .container{
    display: flex;
  }

  .responsive body#top.blog .sidebar ,
  #top.wp-singular .sidebar{
    position: -webkit-sticky !important;
    position: sticky !important;
    top: 180px;
    align-self: flex-start;
    flex: 0 1 30%
  }
}

but that does not work with following sections under the sticky container.