Instread of using metrics, You may use the SimpleCard via KWidget like following:

<?php

class OrderNetMetric extends \koolreport\dashboard\widgets\KWidget
{
    protected function onCreated()
    {
        $this->use(\koolreport\amazing\SimpleCard::class);
    }

    protected function onRendering()
    {
        $range = $this->sibling("DateRange")->value();
        $value = Incognito::rawSQL("
            SELECT
                orderTotal - orderTax - orderShipping - orderShippingTax - cartDiscount - cartDiscountTax - refundAmount AS orderNet
            FROM 
                viuInvoicesRefundsByDate
            WHERE 
                transactionDateTimestamp between '" . $range[0] . "' and '" . $range[1] . "'	
        ")
        ->run()
        ->getScalar(); //Query to get value only

        $this->settings([
            "title"=>"Order Net"
            "value"=>$value
        ]);
        
        return true;
    }
}

Let us know if you need further assistance.

Yes, it is possible, you can use the CustomBoard in which you have full control of the view, you can use HTML or PHP or any KoolReport widget there. It is designed following MVC pattern. The CustomBoard is the closest to the normal KoolReport.