public with sharing class AccountController {
    @AuraEnabled(cacheable=true)
    public static List<Account> getAccountList() {
        return [SELECT Id, Name FROM Account WITH SECURITY_ENFORCED LIMIT 10];
    }
}

public with sharing class ContactController {
    @AuraEnabled(cacheable=true)
    public static List<Contact> getContactList() {
        return [SELECT Id, Name, Title, Phone, Email FROM Contact WITH SECURITY_ENFORCED LIMIT 10];
    }
}

import { LightningElement, track } from "lwc";
import getContactLists from "@salesforce/apex/ContactController.getContactList";
import getAccountLists from "@salesforce/apex/AccountController.getAccountList";
export default class XlsxDemo extends LightningElement {
  @track xlsHeader = []; // store all the headers of the the tables
  @track workSheetNameList = []; // store all the sheets name of the the tables
  @track xlsData = []; // store all tables data
  @track filename = "nikhil_demo.xlsx"; // Name of the file
  @track accountData = []; // used only for storing account table
  @track contactData = []; // used only for storing contact table

  connectedCallback() {
    //apex call for bringing the contact data  
    getContactLists()
      .then(result => {
        console.log(result);
        this.contactHeader = Object.keys(result[0]);
        this.contactData = [...this.contactData, ...result];
        this.xlsFormatter(result, "Contacts");
      })
      .catch(error => {
        console.error(error);
      });
    //apex call for bringing the account data  
    getAccountLists()
      .then(result => {
        console.log(result);
        this.accountHeader = Object.keys(result[0]);
        this.accountData = [...this.accountData, ...result];
        this.xlsFormatter(result, "Accounts");
      })
      .catch(error => {
        console.error(error);
      });
  }

  // formating the data to send as input to  xlsxMain component
  xlsFormatter(data, sheetName) {
    let Header = Object.keys(data[0]);
    this.xlsHeader.push(Header);
    this.workSheetNameList.push(sheetName);
    this.xlsData.push(data);
  }

   // calling the download function from xlsxMain.js 
  download() {
    this.template.querySelector("c-xlsx-main").download();
  }
}

//xlsxMain.js
import { LightningElement, api } from "lwc";
import { loadScript } from "lightning/platformResourceLoader";
import workbook from "@salesforce/resourceUrl/xlsx";
export default class XlsxMain extends LightningElement {
  @api headerList;
  @api filename;
  @api worksheetNameList;
  @api sheetData;
  librariesLoaded = false;
  renderedCallback() {
    console.log("renderedCallback xlsx");
    if (this.librariesLoaded) return;
    this.librariesLoaded = true;
    Promise.all([loadScript(this, workbook + "/xlsx.full.min.js")])
      .then(() => {
        console.log("success");
      })
      .catch(error => {
        console.log("failure");
      });
  }
  @api download() {
    const XLSX = window.XLSX;
    let xlsData = this.sheetData;
    let xlsHeader = this.headerList;
    let ws_name = this.worksheetNameList;
    let createXLSLFormatObj = Array(xlsData.length).fill([]);
    //let xlsRowsKeys = [];
    /* form header list */
      xlsHeader.forEach((item, index) => createXLSLFormatObj[index] = [item])

    /* form data key list */
      xlsData.forEach((item, selectedRowIndex)=> {
          let xlsRowKey = Object.keys(item[0]);
          item.forEach((value, index) => {
              var innerRowData = [];
              xlsRowKey.forEach(item=>{
                  innerRowData.push(value[item]);
              })
              createXLSLFormatObj[selectedRowIndex].push(innerRowData);
          })

      });
    /* creating new Excel */
    var wb = XLSX.utils.book_new();

    /* creating new worksheet */
    var ws = Array(createXLSLFormatObj.length).fill([]);
    for (let i = 0; i < ws.length; i++) {
      /* converting data to excel format and puhing to worksheet */
      let data = XLSX.utils.aoa_to_sheet(createXLSLFormatObj[i]);
      ws[i] = [...ws[i], data];

      /* Add worksheet to Excel */
      XLSX.utils.book_append_sheet(wb, ws[i][0], ws_name[i]);
    }

    /* Write Excel and Download */
    XLSX.writeFile(wb, this.filename);
  }
}