Solution
A Netsuite Email template using HTML. This is being send as email body on PO.
When link is clicked, suitelet is called to perform the action.
<html><head></head><body>
<p><span style="font-family:NotoSans,sans-serif;">Hi ${transaction.entity},</span></p>
<p><span style="font-family:NotoSans,sans-serif;">Please click on the following link to acknowledge your <strong>Purchase Order ${transaction.tranid} </strong></span></p>
<#assign poId=transaction.id/><#assign suiteletURL='https://4856011.extforms.netsuite.com/app/site/hosting/scriptlet.nl?script=939&deploy=1&compid=4856011&h=c2ea2fc0f271f10e569a' + '&po_id=' + poId/>
<p><span style="font-family:NotoSans,sans-serif;"><a href="${suiteletURL}">Click here to acknowledge the Purchase Order</a></span></p>
<p><span style="font-family:NotoSans,sans-serif;">Thank you</span></p>
</body></html>Suitelet Code
/**
 * @NApiVersion 2.1
 * @NScriptType Suitelet
 * 
 *  * MegaResistors-USA-NS
 * MEGR-128: PO Acknowledgement solution
 * ***************************************************************
 * 
 * Author: Jobin and Jismi IT Services
 * Date Created: 3/5/2023
 * Description: This script is used to handle the acknowledgement link click and update the corresponding PO as acknowledged by vendor
 * 
 * REVISION HISTORY
 * @version 1.0: MEGR-128: This script is used to handle the acknowledgement link click and update the corresponding PO as acknowledged by vendor
 */
define(['N/record', 'N/ui/serverWidget'],
    /**
 * @param{record} record
 */
    (record, serverWidget) => {
        /**
         * Defines the Suitelet script trigger point.
         * @param {Object} scriptContext
         * @param {ServerRequest} scriptContext.request - Incoming request
         * @param {ServerResponse} scriptContext.response - Suitelet response
         * @since 2015.2
        */
        const onRequest = (scriptContext) => {
            try {
                if (scriptContext.request.method === 'GET') {
                    const form = serverWidget.createForm({
                        title: ' ',
                    });
                    let alert = form.addField({
                        id: 'custpage_alert',
                        type: serverWidget.FieldType.INLINEHTML,
                        label: 'Alert'
                    });
                    alert.defaultValue = '<script>alert("Thank you! Your PO has been acknowledged successfully");window.close();</script>';
                    const poId = scriptContext.request.parameters.po_id
                    if (poId) {
                        //set 'Purchase Order Acknowledged by Vendor' to checked 
                        record.submitFields({
                            type: record.Type.PURCHASE_ORDER,
                            id: poId,
                            values: {
                                'custbody_jj_po_acknldge_vend_megr128': true
                            },
                            options: {
                                ignoreMandatoryFields: true
                            }
                        });
                    }
                    scriptContext.response.writePage(form);
                }
            } catch (e) {
                //set error message to the PO field
                record.submitFields({
                    type: record.Type.PURCHASE_ORDER,
                    id: poId,
                    values: {
                        'custbody_jj_err_email_snding_megr128': e.message
                    },
                    options: {
                        ignoreMandatoryFields: true
                    }
                });
                log.error("Err@request", e.message)
            }
        }
        return {
            onRequest: onRequest,
        }
    });