Set category in link

Will allow adding category in page url

https://mysite.com/wp-admin/post-new.php?post_title=mytitle&category=mycat

Add to functions.php

function set_category () {

    global $post;
  //Check for a category parameter in our URL, and sanitize it as a string
    $category_slug = filter_input(INPUT_GET, 'category', FILTER_SANITIZE_STRING, array("options" => array("default" => 0)));

  //If we've got a category by that name, set the post terms for it
    if ( $category = get_category_by_slug($category_slug) ) {
        wp_set_post_terms( $post->ID, array($category->term_id), 'category' );
    }

}

//hook it into our post-new.php specific action hook
add_action( 'admin_head-post-new.php', 'set_category', 10, 1 );