Different rendering of an iframe across different platforms

[drdrang]

In a blog post I published yesterday, I included an embedded Mathematica notebook that's linked to the Wolfram Cloud. The code for the embedded notebook is this:

<iframe src="https://www.wolframcloud.com/obj/drdrang0/Published/Plotting%20test.nb?_embed=iframe" width="100%" height="650"></iframe>

When I looked at my feed in NetNewsWire on iOS, I saw that the embedded notebook is rendered just as it on the blog's web page:

But when I look at the feed in NNW on iPadOS or macOS, I see this:

(Clicking "continue anyway" link doesn't do anything.)

The "browser not supported" language suggests that NNW is identifying itself differently across the different platforms. Is that correct? If so, should that be the case? And is there anything I can do to get the Mac and iPad versions to render the way the iPhone version does?