How do I fix this ‘Undefined variable:’ debug message?

Works for me

global $wp_query;

if ( function_exists( 'pagination' ) ) {
    pagination( $wp_query->max_num_pages ); 
}else {
    // Previous/next page navigation.
    the_posts_pagination( array(
        'prev_text'          => __( 'Previous' ),
        'next_text'          => __( 'Next' ),
        'screen_reader_text' => __( ' ' )
        //'before_page_number' => '<span class="meta-nav screen-reader-text">' . __( 'Page' ) . ' </span>',
    ));
};