function single_screen_columns( $columns ) {
    $columns['dashboard'] = 1;
    return $columns;
}
add_filter( 'screen_layout_columns', 'single_screen_columns' );
function single_screen_dashboard(){return 1;}
add_filter( 'get_user_option_screen_layout_dashboard', 'single_screen_dashboard' );

Display dashboard in a single column only

php, wordpress

PHP