How iframe affect SEO in 2022?

Question

Say, we have two static pages: index.html and content.html.

index.html looks like this:

<div>Some static template...</div>
<iframe src="content.html"></iframe>

Question: will Google parse the whole website including content.html and show that in search previews?

I read this question https://stackoverflow.com/questions/8988855/include-another-html-file-in-a-html-file but most people suggest fetching data from JS. I am not SEO, but as I understand, the content either won't be parsed by robots or won't be ranked on top.

Am I correct? Are there any other suggestions how to make it SEO friendly?

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1. Most questions are really old like this one Does iframe affect SEO of its parent page?
2. The page content.html is hosted on the same domain!
3. Ideally, I want to override content.html occasionally but it is essential the text on this page to be crawled.
4. My idea is to host a static website on Amazon S3 and update content via API. It is fast, cheap and easy to maintain.