Source code for https://victorfont.com/limit-number-of-posts-in-query/

vmf_limit_main_posts.php

<?php

function vmf_limit_main_search_posts( $limit, $query ) {

	if ( ! is_admin() && $query->is_main_query() ) {
		return 'LIMIT 0, 40';
	}

	return $limit;
}
add_filter( 'post_limits', 'vmf_limit_main_posts', 10, 2 );

vmf_limit_search_posts.php

<?php

function vmf_limit_main_search_posts( $limit, $query ) {

	if ( ! is_admin() && $query->is_search() ) {
		return 'LIMIT 0, 40';
	}

	return $limit;
}
add_filter( 'post_limits', 'vmf_limit_search_posts', 10, 2 );