WP_Query Filtred by author name ( Return null )

Question

That’s not how WP_Query works, it isn’t what the documentation says either. WP_Query is not a function.

foreach needs an array, or something that can be iterated on, but you’ve given it a WP_Query object.

Instead, look at the documentation or tutorials, all of them follow this basic pattern for a standard post loop:

$args = [
    // parameters go here
];
$query = new WP_Query( $args );
if ( $query->have_posts() ) { 
    while ( $query->have_posts() ) {
        $query->the_post();
        // display the post
        the_title();
        the_content();
    }
    wp_reset_postdata();
} else {
    echo "no posts were found";
}