I didn't understand the last paragraph in your post.
So, can't you just make two slides visible at the desktop breakpoint and the other six invisible using Display - None.
Then at the mobile breakpoint make the six slides visible and set the other two invisible using Display - None.
Will that not work for you?
The problem now is that you will have to wait for CoffeeCup to answer to my last post as to whether or not this can be done to entire slides and not just to a(n) element(s) in a slide. And, you will have to wait for the next version of the RCS software to fix the general problem of Display - None causing slideshows to freeze up.

I laugh at myself now, not sure because of my poor english or my poor brain says something else but my hand writes differently, Don't LoL ok it's the sign of aging

What I mean is :
I don't think if its practical or right choice to set display None for many slides

I was thinking of using in old fashion way to separate URLs slides structure which devices are detected by investigating the HTTP headers and then redirected either to a desktop or mobile version of the slides which are built with different HTML and CSS and not sure in other hand how it behaves with whole things get embedded into another site for instance RSD .

I am sure there is many other way to handle this issue, let see what they are brewing for us in next version, maybe things gets better.

To answer your question:

I can set display None for slides there is no problem, and in process I also notice the freezing issue or big gap of timing when slides tries to move from one slide to anther slides and that's made me thinking maybe this method its not right and cracking my head to achieving something different.

I hope I am clear now.

I think the method of making slides visible and invisible at different breakpoints will do what you desire to happen. But, did you read my last paragraph that says it won't work now because of the freezing issue? You will have to wait to try it in Version 1.1 where CoffeeCup says that the freezing problem is fixed.

Yes I am aware of freezing issue and thank you for your help on this matter.