@RickR2H I can't reproduce this on a clean, new installation of current 4.0-dev. In this case, the "Attachments Folder" option in the Media Manager component's options is empty, so there is no "+" button shown in any of the mail templates to add an attachment.

So my questions are:

1. Have you used a new installation of current 4.0-dev or latest nightly? Or have you used an installation which was updated in past? If so, please let us know the update history.
2. What is the value of the "Attachments Folder" option in the Media Manager component's options of your installation?

@richard67 I can confirm the issue. Currently, look like subform is not working at all. For example, we can add a new custom field checkbox and could not add options for the custom field anymore

I got the issue reported by @RickR2H if i set in options of mail templates the Attachment Folder to images.

I got the issue reported by @RickR2H if i set in options of mail templates the Attachment Folder to images.

Confirmed.

@richard67 I can confirm the issue. Currently, look like subform is not working at all. For example, we can add a new custom field checkbox and could not add options for the custom field anymore

@joomdonation Last change for subforms in J4 was #31567 . Could it be related to that PR? Or has the upmerge from 3.10-dev broken something from that PR?

@joomdonation Could you open an issue for the general subforms issue and we make it a release blocker? Or should we use this issue here to continue and make it a release blocker?

@richard67 We could use this issue here to continue. I don't know subform code enough to confirm where this issue comes from. Maybe @Fedik could help ?

I will try to look what's going on

Sorry @dgrammatiko . Look like it causes by Joomla.sanitizeHtml too. If we change this line of code to https://github.com/joomla/joomla-cms/blob/4.0-dev/build/media_source/system/js/fields/joomla-field-subform.w-c.es6.js#L186 to :

tmpEl.innerHTML = this.template;

The issue is gone. Could you please look at this?

@Fedik probably it's coming from the sanitiser: https://github.com/dgrammatiko/joomla-cms/blob/bdf673b3c7c82b819b8e97608ceef41325c06d3c/build/media_source/system/js/fields/joomla-field-subform.w-c.es6.js#L186

Ah, we added comment at the same time :).

@joomdonation here's a PR: #34514

Fixed on PR #34514 , so closing this issue.