Negative effect of using display:none for duplicate content

So i'm using display: none for mobile when viewed on desktop and the other way around, purposely for layout and visible only, they serve the same content. Does this consider as duplicate or keyword stuffing

nope, you're safe. That's how you should do it anyway, to tell google which content is for which environment, so you're good...
Secondly (and on the topic itself), display:none is still not dangerous, but I should have mentioned in the previous post that this piece of code alone might not be enough to display the versions properly, so be sure that you're using the complete and right code)