Comment count next to post title?

On most cases you should be able to use the_title filter to modify the title string. Use get_comments_number() to get the comments count for the post – of given ID or the current one.

For example,

add_filter( 'the_title', 'wpse_427277_the_title', 10, 2 );
function wpse_427277_the_title( string $title, $post_id = null ): string {
    $comment_count = (int) get_comments_number( $post_id );
    if ( $comment_count ) {
        $title .= sprintf( ' (%d)', $comment_count );
    }

    return $title;
}

Modify as needed.