Publishing Responsive Project for Website Which is Scalable

Rod is correct, creating a fluid boxes project is only a good idea if the majority of your learners will access the course with a mobile device and want to be able to use both portrait and landscape view. Using Position Properties, which is possible since version 11.5 can improve the experience, but still you are limited to the original project size, which you may choose to increase (with all its consequences about file size of course).

The biggest drawback for a Scalable non-responsive project is that it should be used in landscape mode. All published outputs in my blog are using Scalable non-responsive projects which makes the experience agreeable on all desktop systems, but it is possible to watch them on a mobile device as well, preferably in Landscape mode. Try one out:

https://www.lilybiri.com/published/tarot/index.html

Responsive projects don't give you the option to use Scalable HTML when publishing.  That checkbox is only present on normal non-responsive projects.

What you are discovering is that responsive projects are mainly intended for viewing on mobile devices.  If your target audience is mainly viewing content on desktop computers, you would be better off building your project as non-responsive because then you can use a larger stage size.  Sometimes the only way to adequately cover both mobile and desktop viewport sizes is to create two projects, one responsive and one normal non-responsive.

Are you certain that there are sufficient numbers of people in your target audience that cannot view the content EXCEPT on their mobile phones?  That would b the only reason (in my view) to have a responsive project at all.