Can you please help me understand what is the differences between Frameless vs HTML5 output. when would i pick one vs the other? Also, is the Frameless output accessible?
In Responsive HTML5, the topic content is displayed inside an iframe. In Frameless, there is no iframe. I think you just pick the one you like the look of most, unless your organisation has some specific technical requirement not to use iframes. From a purely non-technical user perspective, I don't see much difference besides aesthetics.
I think both outputs are supposed to be 508 compliant, which I think it a US government accessibility requirement. I can't comment first-hand on the accessibility though.
See the end of this page http://www.grainge.org/pages/authoring/rh_tour/rh2020/outputs/skin_editor.htm for information about accessibility in RoboHelp 2020.