Remove Specific Post Categories from the Blog Index

remove-categories-blog-index.php

<?php //* mind this opening php tag

//* Exclude categories from blog page
add_filter('pre_get_posts', 'rv_exclude_blog_categories');
function rv_exclude_blog_categories($query) {
	if ($query->is_home) {
		$query->set('cat', '-1,-2,-3'); //Replace with your category numbers (keep negative signs)
	}
	return $query;
}