See https://ithoughthecamewithyou.com/post/how-to-backup-google-photos-to-google-drive-automatically-after-july-2019-with-apps-script#d582cd15-aa3c-427b-a3b9-0f585192a321

Code.gs

// script settings
//
// https://ithoughthecamewithyou.com/post/how-to-backup-google-photos-to-google-drive-automatically-after-july-2019-with-apps-script
//
var ClientID = '';
var ClientSecret = '';
var BackupFolder = 'Google Photos';

function onOpen() {
  var ui = SpreadsheetApp.getUi();
  ui.createMenu('Google Photos Backup')
      .addItem('Authorize if needed (does nothing if already authorized)', 'showSidebar')
      .addItem('Backup Now', 'runBackup')
      .addItem('Reset Settings', 'clearProps')
      .addToUi();
}

function runBackup() {
  var photos = getPhotosService();
 
  var nextPageToken = null;
  var downloadList = [];

  // Limit of around 10,000 photos
  for (var page = 1; page <= 1000; page++) {
    Logger.log('Requesting page ' + page);

    var MILLIS_PER_MINUTE = 60000;
    var MILLIS_PER_HOUR = MILLIS_PER_MINUTE * 60;
    var MILLIS_PER_DAY = MILLIS_PER_HOUR *24;
   
    var now = new Date();
    var from = new Date(now.getTime() - MILLIS_PER_DAY)
    var tomo = new Date(now.getTime() + MILLIS_PER_DAY)
   
   
    var request = {
      "pageSize":"100",
      "filters": {
        "dateFilter": {
          "ranges": [
            {
              "startDate": {
                "year": from.getFullYear(),
                "month": from.getMonth() + 1,
                "day": from.getDate()
              },
              "endDate": {
                "year": tomo.getFullYear(),
                "month": tomo.getMonth() + 1,
                "day": tomo.getDate()
              }
            }
          ]
        }
      }
    };
     
    if (nextPageToken != null) {
      request["pageToken"] = nextPageToken;
    }
   
    var response = UrlFetchApp.fetch('https://photoslibrary.googleapis.com/v1/mediaItems:search', {
      headers: {
        Authorization: 'Bearer ' + photos.getAccessToken()
      },
      'method' : 'post',
      'contentType' : 'application/json',
      'payload' : JSON.stringify(request, null, 2)
    });
     
    var json = JSON.parse(response.getContentText());
   
    if ('mediaItems' in json) {
      var photoCount = json.mediaItems.length;
      for (var i = 0; i < photoCount; i++) {
        var filename = json.mediaItems[i].filename;
        var baseUrl = json.mediaItems[i].baseUrl;
        if ('photo' in json.mediaItems[i].mediaMetadata) {
          // if the photo property exists it's a photo and use =d to download, otherwise a video and we need to use =dv
          baseUrl += '=d';
        } else {
          baseUrl += '=dv';
        }
        downloadList.push({
          "filename" : filename,
          "baseUrl" : baseUrl
        });
      }
    }
   
    if ('nextPageToken' in json) {
      nextPageToken = json.nextPageToken;
    } else {
      break;
    }
  }
 
  var folder;
  var folders = DriveApp.getFoldersByName(BackupFolder);
  while (folders.hasNext()) {
    folder = folders.next();
    break;
  }
 
  var downloadCount = downloadList.length;
  for (var i = 0; i < downloadCount; i++) {
    var filename = downloadList[i].filename;
    Logger.log('Downloading ' + downloadList[i].filename);

    var response = UrlFetchApp.fetch(downloadList[i].baseUrl, {
      headers: {
        Authorization: 'Bearer ' + photos.getAccessToken()
      }
    });
    var files = folder.getFilesByName(filename);
    if (!files.hasNext()) {
      var blob = response.getBlob();
      blob.setName(filename);
      folder.createFile(blob);
    }
  }
}

// functions below adapted from Google OAuth example at https://github.com/googlesamples/apps-script-oauth2

function getPhotosService() {
  // Create a new service with the given name. The name will be used when
  // persisting the authorized token, so ensure it is unique within the
  // scope of the property store.
  return OAuth2.createService('photos')

      // Set the endpoint URLs, which are the same for all Google services.
      .setAuthorizationBaseUrl('https://accounts.google.com/o/oauth2/auth')
      .setTokenUrl('https://accounts.google.com/o/oauth2/token')

      // Set the client ID and secret, from the Google Developers Console.
      .setClientId(ClientID)
      .setClientSecret(ClientSecret)

      // Set the name of the callback function in the script referenced
      // above that should be invoked to complete the OAuth flow.
      .setCallbackFunction('authCallback')

      // Set the property store where authorized tokens should be persisted.
      .setPropertyStore(PropertiesService.getUserProperties())

      // Set the scopes to request (space-separated for Google services).
      // see https://developers.google.com/fit/rest/v1/authorization for a list of Google Fit scopes
      .setScope('https://www.googleapis.com/auth/photoslibrary.readonly')

      // Below are Google-specific OAuth2 parameters.

      // Sets the login hint, which will prevent the account chooser screen
      // from being shown to users logged in with multiple accounts.
      .setParam('login_hint', Session.getActiveUser().getEmail())

      // Requests offline access.
      .setParam('access_type', 'offline')

      // Forces the approval prompt every time. This is useful for testing,
      // but not desirable in a production application.
      //.setParam('approval_prompt', 'force');
}

function showSidebar() {
  var photos = getPhotosService();
  if (!photos.hasAccess()) {
    var authorizationUrl = photos.getAuthorizationUrl();
    var template = HtmlService.createTemplate(
        '<a href="<?= authorizationUrl ?>" target="_blank">Authorize</a>. ' +
        'Close this after you have finished.');
    template.authorizationUrl = authorizationUrl;
    var page = template.evaluate();
    SpreadsheetApp.getUi().showSidebar(page);
  } else {
  // ...
  }
}

function authCallback(request) {
  var photos = getPhotosService();
  var isAuthorized = photos.handleCallback(request);
  if (isAuthorized) {
    return HtmlService.createHtmlOutput('Success! You can close this tab.');
  } else {
    return HtmlService.createHtmlOutput('Denied. You can close this tab');
  }
}

function clearProps() {
  PropertiesService.getUserProperties().deleteAllProperties();
}