Well, here's an interesting twist! If you use Wordpress, the Amazon book preview is still available to you.
If you're using the Gutenberg editor, click to add a block and pick Amazon Kindle. Then insert the link for the product page for which you want the book preview.
When this feature was first released, it didn't support affiliate codes, but now, it evidently does. If you're an affiliate, go to the affiliate site stripe on the page for which you want a preview, click Text under Get Link and then select full link. Copy the result into the link area in the Amazon Kindle block. Presto!
If you're using a different page builder (like I use Elementor, for example), Follow the steps above in Gutenberg, switch to code view, copy the code from the Amazon Kindle block you just made, open a new post to edit in your page builder, switch to code or text view, and paste in the code you got from Gutenberg. It worked for me in Elementor, so it should work for you.
There are plugins that enable you to use Gutenberg blocks directly in Elementor (and probably other page builders), so you could skip the steps in the last paragraph. However, all the ones I saw that did that were paid plugins.