I also found this script and it works in gmail.
But the company uses outlook, and the email will not work with gmail, hence why I have to find a MS based solution.

// To learn how to use this script, refer to the documentation:
// Create a mail merge with Gmail & Google Sheets | Apps Script | Google Developers

/*
Copyright 2022 Martin Hawksey

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

/**
* @OnlyCurrentDoc
*/

/**
* Change these to match the column names you are using for email
* recipient addresses and email sent column.
*/
const RECIPIENT_COL = "Recipient";
const EMAIL_SENT_COL = "Email Sent";

/**
* Creates the menu item "Mail Merge" for user to run scripts on drop-down.
*/
function onOpen() {
const ui = SpreadsheetApp.getUi();
ui.createMenu('Mail Merge')
.addItem('Send Emails', 'sendEmails')
.addToUi();
}

/**
* Sends emails from sheet data.
* @param {string} subjectLine (optional) for the email draft message
* @param {Sheet} sheet to read data from
*/
function sendEmails(subjectLine, sheet=SpreadsheetApp.getActiveSheet()) {
// option to skip browser prompt if you want to use this code in other projects
if (!subjectLine){
subjectLine = Browser.inputBox("Mail Merge",
"Type or copy/paste the subject line of the Gmail " +
"draft message you would like to mail merge with:",
Browser.Buttons.OK_CANCEL);

if (subjectLine === "cancel" || subjectLine == ""){
// If no subject line, finishes up
return;
}
}

// Gets the draft Gmail message to use as a template
const emailTemplate = getGmailTemplateFromDrafts_(subjectLine);

// Gets the data from the passed sheet
const dataRange = sheet.getDataRange();
// Fetches displayed values for each row in the Range HT Andrew Roberts
// A bulk email/mail merge with Gmail and Google Sheets solution evolution using V8 – By @mhawksey
// @see Class Range | Apps Script | Google Developers
const data = dataRange.getDisplayValues();

// Assumes row 1 contains our column headings
const heads = data.shift();

// Gets the index of the column named 'Email Status' (Assumes header names are unique)
// @see Page not found - Desktop Liberation
const emailSentColIdx = heads.indexOf(EMAIL_SENT_COL);

// Converts 2d array into an object array
// See javascript: convert two dimensional array to array of objects using the first 'row' to define properties - Stack Overflow
// For a pretty version, see Google Apps Script Patterns: Using the destructuring assignment syntax and object arrays to process Google Sheet rows – By @mhawksey
const obj = data.map(r => (heads.reduce((o, k, i) => (o[k] = r[i] || '', o), {})));

// Creates an array to record sent emails
const out = [];

// Loops through all the rows of data
obj.forEach(function(row, rowIdx){
// Only sends emails if email_sent cell is blank and not hidden by a filter
if (row[EMAIL_SENT_COL] == ''){
try {
const msgObj = fillInTemplateFromObject_(emailTemplate.message, row);

// See https://developers.google.com/apps-s...,String,Object)
// If you need to send emails with unicode/emoji characters change GmailApp for MailApp
// Uncomment advanced parameters as needed (see docs for limitations)
GmailApp.sendEmail(row[RECIPIENT_COL], msgObj.subject, msgObj.text, {
htmlBody: msgObj.html,
// bcc: 'a.bbc@email.com',
// cc: 'a.cc@email.com',
// from: 'dipesh.shah1@nhs.net',
name: 'SHAH PHARMACY',
replyTo: 'dipesh.shah1@nhs.net',
// noReply: true, // if the email should be sent from a generic no-reply email address (not available to gmail.com users)
attachments: emailTemplate.attachments,
inlineImages: emailTemplate.inlineImages
});
// Edits cell to record email sent date
out.push([new Date()]);
} catch(e) {
// modify cell to record error
out.push([e.message]);
}
} else {
out.push([row[EMAIL_SENT_COL]]);
}
});

// Updates the sheet with new data
sheet.getRange(2, emailSentColIdx+1, out.length).setValues(out);

/**
* Get a Gmail draft message by matching the subject line.
* @param {string} subject_line to search for draft message
* @return {object} containing the subject, plain and html message body and attachments
*/
function getGmailTemplateFromDrafts_(subject_line){
try {
// get drafts
const drafts = GmailApp.getDrafts();
// filter the drafts that match subject line
const draft = drafts.filter(subjectFilter_(subject_line))[0];
// get the message object
const msg = draft.getMessage();

// Handles inline images and attachments so they can be included in the merge
// Based on https://stackoverflow.com/a/65813881/1027723
// Gets all attachments and inline image attachments
const allInlineImages = draft.getMessage().getAttachments({includeInlineIm ages: true,includeAttachments:false});
const attachments = draft.getMessage().getAttachments({includeInlineIm ages: false});
const htmlBody = msg.getBody();

// Creates an inline image object with the image name as key
// (can't rely on image index as array based on insert order)
const img_obj = allInlineImages.reduce((obj, i) => (obj[i.getName()] = i, obj) ,{});

//Regexp searches for all img string positions with cid
const imgexp = RegExp('<img.*?src="cid.*?)".*?alt="(.*?)"[^\>]+>', 'g');
const matches = [...htmlBody.matchAll(imgexp)];

//Initiates the allInlineImages object
const inlineImagesObj = {};
// built an inlineImagesObj from inline image matches
matches.forEach(match => inlineImagesObj[match[1]] = img_obj[match[2]]);

return {message: {subject: subject_line, text: msg.getPlainBody(), html:htmlBody},
attachments: attachments, inlineImages: inlineImagesObj };
} catch(e) {
throw new Error("Oops - can't find Gmail draft");
}

/**
* Filter draft objects with the matching subject linemessage by matching the subject line.
* @param {string} subject_line to search for draft message
* @return {object} GmailDraft object
*/
function subjectFilter_(subject_line){
return function(element) {
if (element.getMessage().getSubject() === subject_line) {
return element;
}
}
}
}

/**
* Fill template string with data object
* @see https://stackoverflow.com/a/378000/1027723
* @param {string} template string containing {{}} markers which are replaced with data
* @param {object} data object used to replace {{}} markers
* @return {object} message replaced with data
*/
function fillInTemplateFromObject_(template, data) {
// We have two templates one for plain text and the html body
// Stringifing the object means we can do a global replace
let template_string = JSON.stringify(template);

// Token replacement
template_string = template_string.replace(/{{[^{}]+}}/g, key => {
return escapeData_(data[key.replace(/[{}]+/g, "")] || "");
});
return JSON.parse(template_string);
}

/**
* Escape cell data to make JSON safe
* @see https://stackoverflow.com/a/9204218/1027723
* @param {string} str to escape JSON special characters from
* @return {string} escaped string
*/
function escapeData_(str) {
return str
.replace(/[\\]/g, '\\\\')
.replace(/["]/g, '\\"')
.replace(/[\/]/g, '\\/')
.replace(/[\b]/g, '\\b')
.replace(/[\f]/g, '\\f')
.replace(/[\n]/g, '\\n')
.replace(/[\r]/g, '\\r')
.replace(/[\t]/g, '\\t');
};
}