If I paste a plain text link (non-hyperlinked) to a post on the same site (using Classic Editor) it converts the post's URL to an iFrame embed.
For example if my site is https://mysite.local and the URL to a product is https://mysite.local/product/test-product-1/, if I paste that product URL into the editor without converting it to a hyperlink, WordPress embeds the URL into an iFrame. I was under the impression WordPress would only do this with known embeddable sites, e.g. YouTube. Does anyone know why this is happening and how to prevent it?
Here is the embed HTML it converts the URL to: