It seems that the problem is that the insert.ExtendAllowedHtml plugin is not being executed due to the condition of the ckeditor_image plugin. I created a patch in the Insert Media submodule with the condition of the media_media plugin, and this resolves the issue.
Hi @snater,
I'm responding to your questions:
The problem is independent of the browser. I have tested it in Chrome and Firefox, and the same issue occurs.
It seems that Drupal.CKEditor5Instances is not loading correctly. When debugging, I see that upon loading the page, insert.js is called, and in FocusManager.js, firstEditorElement is null, so it selects the textarea from the summary.
When clicking the media insert button, it is already predefined to add the media in the summary field, whether or not the focus is on the body field.
crisgc → created an issue.
Rename patch: Adding additional special characters to the regex for replacement
Adding additional special characters to the regex for replacement