Query groups by incomplete name

We have 160 groups and 3800 users. The Email Users plugin is trying to load all groups and users on page load. We are trying to integrate select2.js so create a searchable select field using ajax as demoed here https://select2.org/data-sources/ajax

Further instructions here https://rudrastyh.com/wordpress/select2-for-metaboxes-with-ajax.html

My question is how would we format the query?

Here is an example but it uses posts…


add_action( 'wp_ajax_mishagetposts', 'rudr_get_posts_ajax_callback' ); // wp_ajax_{action}
function rudr_get_posts_ajax_callback(){

// we will pass post IDs and titles to this array
$return = array();

// you can use WP_Query, query_posts() or get_posts() here – it doesn’t matter
$search_results = new WP_Query( array(
‘s’=> $_GET[’q’], // the search query
‘post_status’ => ‘publish’, // if you don’t want drafts to be returned
‘ignore_sticky_posts’ => 1,
‘posts_per_page’ => 50 // how much to show at once
) );
if( $search_results->have_posts() ) :
while( $search_results->have_posts() ) : $search_results->the_post();
// shorten the title a little
$title = ( mb_strlen( $search_results->post->post_title ) > 50 ) ? mb_substr( $search_results->post->post_title, 0, 49 ) . ‘…’ : $search_results->post->post_title;
$return[] = array( $search_results->post->ID, $title ); // array( Post ID, Post Title )
endwhile;
endif;
echo json_encode( $return );
die;
}