How can I make this JavaScript code get executed when the BigPipe module is enabled?

I keep struggling with getting JavaScript executed when I need to target a DOM element that is added via the BigPipe module when I'm logged in on my Drupal site.

The following code runs when I'm not logged in, but it's never executed when I am logged in.

(function ($) {
  'use strict';

  Drupal.behavior.bpBlockTest = {
    attach: function(context, settings) {
      $('.my-block', context).once('bp-block-testing').each(function () {
        var $myBlock = $(this);
        var $addOn = $('<span>addOn</span>');
        $addOn.appendTo($myBlock);
      });
    }
  }

}(jQuery));

For the current Drupal version this is the correct way to run Javascript (including jQuery, Drupal and the new Drupal once library):

(function ($, Drupal, once) {
  Drupal.behaviors.myModuleBehavior = {
    attach: function (context, settings) {
      once('myCustomBehavior', 'input.myCustomBehavior', context).forEach(function (element) {
        // Apply the myCustomBehaviour effect to the elements only once.
      });
    }
  };
})(jQuery, Drupal, once);

MODULE.libraries.yml or THEME.libraries.yml:

foobar:
  js:
    js/foobar.js: {}
  dependencies:
    - core/drupal
    - core/jquery
    - core/once

From https://www.drupal.org/docs/drupal-apis/javascript-api/javascript-api-overview

See also https://www.drupal.org/node/3158256

Until #3272693 is fixed, the fix for this is to remove context from your once function or use $.filter()

(function ($, Drupal, once) {
  Drupal.behaviors.myBehavior = {
    attach: function (context, settings) {
      // don't use context with once
      once('myBehavior', '.myBehavior').forEach(function (element) {});
      // or use filter
      $(context).filter('.myBehavior').once('myBehavior').forEach(function (element) {});
    }
  };
})(jQuery, Drupal, once);