See https://ithoughthecamewithyou.com/post/automate-google-pagespeed-insights-with-apps-script

PageSpeed.gs

var apiKey = '';
var monitorUrl = '';
var originUrl = '';

function monitor() {
  // CRUX
  var allCrux = callCrux(null, originUrl);
  var desktopCrux = callCrux('DESKTOP', originUrl);
  var mobileCrux = callCrux('MOBILE', originUrl);

  // Pagespeed Insights
  var desktop = callPageSpeed('desktop', monitorUrl);
  var mobile = callPageSpeed('mobile', monitorUrl);

  var spreadsheet = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = spreadsheet.getSheetByName('results');

  sheet.appendRow([
                   Utilities.formatDate(new Date(), 'GMT', 'yyyy-MM-dd'),
                   desktop.lighthouseResult.categories.performance.score * 100,
                   desktopCrux.lcp == -1 ? (allCrux.lcp == -1 ? ' ' :allCrux.lcp) : desktopCrux.lcp,
                   desktopCrux.inp == -1 ? (allCrux.inp == -1 ? ' ' :allCrux.inp) : desktopCrux.inp,
                   desktopCrux.cls == -1 ? (allCrux.cls == -1 ? ' ' :allCrux.cls) : desktopCrux.cls,
                   mobile.lighthouseResult.categories.performance.score * 100,
                   mobileCrux.lcp == -1 ? (allCrux.lcp == -1 ? ' ' :allCrux.lcp) : mobileCrux.lcp,
                   mobileCrux.inp == -1 ? (allCrux.inp == -1 ? ' ' :allCrux.inp) : mobileCrux.inp,
                   mobileCrux.cls == -1 ? (allCrux.cls == -1 ? ' ' :allCrux.cls) : mobileCrux.cls
                  ]);
    
    // much more available, i.e. desktop.pageStats.numberResources
}

function callCrux(strategy, origin) {
  var lcp = -1;
  var inp = -1;
  var cls = -1;

  var cruxUrl = 'https://chromeuxreport.googleapis.com/v1/records:queryRecord?key=' + apiKey;
  var payload = {
    "origin": origin,
    "metrics": [
      "largest_contentful_paint",
      "cumulative_layout_shift",
      "interaction_to_next_paint"
    ]
  };
  if (strategy) {
    payload["formFactor"] = strategy;
  }
  var options = {
    method: 'post',
    contentType: 'application/json',
    payload: JSON.stringify(payload),
  };

  try {
    var response = UrlFetchApp.fetch(cruxUrl, options);
    var json = JSON.parse(response.getContentText());

    if ('largest_contentful_paint' in json.record.metrics) {
      lcp = parseFloat(json.record.metrics.largest_contentful_paint.percentiles.p75) / 1000.0;
    }

    if ('cumulative_layout_shift' in json.record.metrics) {
      cls =  parseFloat(json.record.metrics.cumulative_layout_shift.percentiles.p75);
    }

    if ('interaction_to_next_paint' in json.record.metrics) {
      inp =  parseFloat(json.record.metrics.interaction_to_next_paint.percentiles.p75) / 1000.0;
    }

  } catch {
    
  }

  return { "cls":cls, "inp":inp, "lcp":lcp  };
}

function callPageSpeed(strategy, url) {
  var pageSpeedUrl = 'https://www.googleapis.com/pagespeedonline/v5/runPagespeed?url=' + url + '&key=' + apiKey + '&strategy=' + strategy;
  var response = UrlFetchApp.fetch(pageSpeedUrl);
  var json = response.getContentText();
  return JSON.parse(json);
}