disable-post-title-wp-query-search.php

<?php

// temporarily disable post_title matching for wp query search
add_filter('posts_where_paged', $disablePostTitleSearch=function( string $sql )
{
    return str_replace('.post_title LIKE ', '.post_content LIKE ', $sql);
});

// now query posts
$posts = query_posts([
    'numberposts' => -1,
    'posts_per_page' => PHP_INT_MAX,
    'post_type' => ['post','page'],
    's' => 'keyword',
]);

// enable back title search for subsequent calls
remove_filter('posts_where_paged', $disablePostTitleSearch);