Is it possible to receive the HTML from the notion-api. The same function as it is in the GUI?
I know that you can get the Page/Block with an request and receive an JSON which you have do present on your own. Is it possible to request a HTML from the notion-api?
No, that's currently not possible.
What you could do: Open your Notion page in the browser (Copy Link), grab the HTML (Inspect) and populate the content through the Notion API.