Issue with integrating microdata into TinyMCE custom fields using Meta Box

Dear Meta Box team,

I have recently encountered an issue while integrating microdata into TinyMCE custom fields using your Meta Box plugin. I hope you can help me resolve this issue.

Here are the details of my problem:

1. I am using the Meta Box plugin to add custom WYSIWYG (TinyMCE) fields in the product editing section on my WordPress site.
2. I would like to retain certain microdata attributes (such as itemscope, itemtype, itemprop, itemid, itemref, and content) within these custom fields.
3. I have tried extending the TinyMCE configuration by adding the valid_elements and extended_valid_elements options, but this did not work.
4. I also tried registering a custom JavaScript file with the TinyMCE configuration and enqueuing it using wp_enqueue_script, but this did not solve the issue either.
5. Despite my attempts, the microdata attributes are not retained when I save a product entry.

Here is the code I am using to add the custom fields with Meta Box:

https://i.postimg.cc/YqCxgC6s/help.jpg

And here is an example of the HTML structure with microdata that I want to use:

https://i.postimg.cc/WjWSLMsR/exemple.jpg

Could you help me find a solution to retain the microdata attributes within the TinyMCE custom fields using Meta Box? If you need any further information, please let me know.

Thank you in advance for your assistance.

Best regards,

Laurent