HTM with embedded content in { }

Has anyone tried to make use of the embedded content function in the HTML file type?

I have a file, where beside the html code such content is included:

<h1>ESG Report{% if preview %} - <strong>Preview</strong>{% endif %}</h1>

As the complete text would perfectly work with HTML, I would like simply to exclude the { } content. So I just assumed, I add this to plain text (I added {{1,2}.*?}{1,2} as inline tag) in the embedded content processors and activate that in the html parser, but id does not work.

So what I am doing wrong here?