my question is pretty self-explanatory, there is any technical or legal issue in selling libgdx games on steam?
It is possible to show some kind of evidence, maybe a exemple of a game that is made with libgdx and already is on steam?
No, there's no technical or legal issue why you can't sell your LibGDX game on Steam.
However -- and this is not specific to any platform or library -- your game needs to be pretty good for it to get their attention.
libgdx is under the apache 2.0 license meaning that you can use it freely in both for-profit, non-profit,open-source and closed source games. Selling a game on steam makes it for-profit and likely closed source so you will be fine as long as you read at least once through the apache 2.0 lisence (it's not that long).