Display in a page a value inside a url after a GET

hello,
I wonder how can I show inside a page, one of the value that are in my url after a form submission with a get method.
I can see the value inside the url, but I don’t know how to show it inside my page, with the Gutenberg editor.

I guess I need something like this, but where to add it? I don’t have a “php code” block type…

echo $_GET[‘param_name’];