Use a .html file uploaded as file from iframe

Hi,

I am trying to use our own little app snippet in a .html file from an iframe in a code block. I have this file on squarespace: https://metaversewebshowcase.squarespace.com/s/showcase.html but when I try to use it from a code block as

<iframe src="https://metaversewebshowcase.squarespace.com/s/showcase.html"/>

I get this. If I open the URL directly in the browser, it simply downloads the file but not open it, so I suspect that there is a content-type is not properly set, or maybe the download attribute is attached for some reason. Changing "Open in a new Window" switch does not affect it.

Can somebody shed light on this, and perhaps tell me how to make the .html file usable as the src of iframe?