Default, openpos use “completed” order status to get report in admin/pos/report.

if you want use your custom order status . you add this snippets code to “yourtheme/functions.php” or use snippets code plugin

function custom_pos_op_order_report_status($statuses){
    $statuses = array('wc-processing'); // change to your custom status
    return $statuses;
}
add_filter('op_order_report_status','custom_pos_op_order_report_status',10,1);