Have you looked at the Responsive HTML5 output?
I am currently using Responsive HTML5 (from RH 2017) and it uses frames. I've tried different layout templates and they all use frames (iframes).
Wow, feels like I'm living many years ago when the web was new. I know that back then, frames were frowned upon because the search engine crawlers had issues crawling the pages inside. But that eventually was overcome.
So I'm surprised to hear that an issue exists with some inability of crawlers to find and index the content. Not to mention the other little fact we so very often see where folks DO NOT WANT their help content to be found by anyone. EVER! And they are asking for ways to prevent that from happening.
Take a read of this article:
Currently the answer is there is no version that does not use frames. However, Adobe is working on it and the tentative timeline is early next year, with no guarantees. This will only be for the 2019 version.
See www.grainge.org for free RoboHelp and Authoring information.
Thank you for the prompt reply.