Can't pass variable to views style plugin template
In below code you preprocess the variables for views-view.html.twig file

function alpha_preprocess_views_view(&amp;$variables) {
  $variables["beta"] = "1";
}


and, function alpha_preprocess_page(&amp;$variables) will preprocess the variables for page.html.twig

So, if you create a file views-view.html.twig then you will get your variable {{ beta }}