Featured Image Fallback

add_filter( 'post_thumbnail_html', 'my_default_featured_image', 10, 5 );

function my_default_featured_image( $html, $post_id, $post_thumbnail_id, $size, $attr ) {

    // If no HTML is generated (no featured image set)

    if ( empty( $html ) ) {

        // Replace with your actual image URL

        $default_image_url = 'https://example.com/path/to/your-default-image.jpg';

        // Generate the HTML for the default image

        $html = sprintf(

            '<img src="%s" alt="Default Featured Image" class="wp-post-image" />',

            esc_url( $default_image_url )

        );

    }

    return $html;

}