Neither timeline nor month view is showing up in node

Same on a fresh Drupal 11 installation. Additionally I get an error when adding events via admin/bat/events/event/add/availability_daily

This was the last jQuery.once left since Drupal 10 update. Moved it to core/once function

This issue is being worked on latest dev, with a more recent Fullcalendar version
Please do not timeline view is now only available with commercial license

In latest 11.1.x we have now a more recent Fullcalendar version.

Fullcalendar Timeline may require a Premium release. See https://fullcalendar.io/license

Ok, So it seems like the bat_calendar_reference.js is

      $('.cal').once().each(function () {
        var lastSource;
        var cal_id = $(this).attr('id');

        $(this).fullCalendar({

which when changed to something like

once('bat-calendar', '.cal', context).forEach(function (el) {
        var lastSource;
        var cal_id = $(this).attr('id');

        $(el).fullCalendar({

solves the JS error in the console but then all the settings from /admin/bat/config/fullcalendar are not read

In order to just see if it works I hardcoded the options:

(function ($, Drupal, once) {
  Drupal.behaviors.bat_calendar_reference = {
    attach: function (context) {
      const businessHours = {
        startTime: '00:00',
        endTime: '24:00',
        daysOfWeek: [0, 1, 2, 3, 4, 5, 6],
      };

      once('bat-calendar', '.cal', context).forEach(function (el) {
        $(el).fullCalendar({
          schedulerLicenseKey: 'GPL-My-Project-Is-Open-Source',
          themeSystem: 'standard',
          locale: 'en',
          editable: false,
          selectable: false,
          nowIndicator: true,
          businessHours: businessHours,
          initialView: 'dayGridMonth', // or 'timeGridWeek', etc.
          events: [], // will be filled automatically if Views integration is working
        });
      });
    }
  };
})(jQuery, Drupal, once);

and now the Calendar is visible. Could it be that In Drupal 10+, once is an ES6 utility and not part of jQuery?

Currently working on this, with events produced by bat_api

Thanks for contributing.

fixed in latest dev. Feedback welcome