Count Post amount per user

/**
 *Count posts of given type, so each user can create post only once
 */
function u_post_count() {
    $user_post_count = count( get_posts( array( 
    'post_type' => 'your_post_type', 
    'author'    => get_current_user_id(), 
) ) );
        
    return $user_post_count;
}

It will count all Posts of the current logged in user.
Make sure to define the Post type in 'post_type'
It returns a numeric count.