Is it possible to add an iframe here?

[ReiArarajuba]

[itxashancode]

[markup]
 [markup.goldmark]
 [markup.goldmark.renderer]
 unsafe = true

Yes, that enables raw HTML. So you can just paste iframe. If not, add to config. Or create a shortcode if you want reusable. In PaperMod you can drop raw HTML straight into your .md files because the theme already sets markup.goldmark.renderer.unsafe = true. Just paste:

<iframe src="https://example.com" width="600" height height