Sometimes you just want to have one check that checks if it’s related to the blog. Yes, this uses many functions, so use it as a last resort.

Check if it’s part of the blog.php

// check if it's a blog page
function is_blog () {
  global  $post;
  $posttype = get_post_type($post );
  return ( ((is_archive()) || (is_author()) || (is_category()) || (is_home()) || (is_single()) || (is_tag())) && ( $posttype == 'post')  );
}