WordPress 7.0 – custom HTML

We use “custom HTML” to insert json structured data on our pages or posts. When we edit the page or post now with WordPress 7, these boxes seem to be empty and even not visible. Only if we click on the space where it should be we can click on “edit code” and then see the content in an overlay. This behaviour is not good. How do we set it back to the former version? The new layout is dangerous, because someone might delete these boxes, when editing the page/post.

The page I need help with: [log in to see the link]