🐛 | Drupal core | An error occurred while attempting to process /node/add/page?_wrapper_format=drupal_ajax: ajax.$form.ajaxSubmit is not a function
Had same issue after updating to Drupal 10.1.1.
Got a custom route that returns AjaxResponse, but for some reason it started to throw the ajax.$form.ajaxSubmit is not a function alert.
After searching it appears that core/jquery.form is being removed at Drupal 10. After digging into the core files, found core/internal.jquery.form is being used instead. After replacing it in the .libraries.yml file of the current theme, it started to work.
Hope that will help someone.