Is Anybody developing for Nintendo Switch SDL2 (libnx)?

Are there some forum to get info?

Yes! But we are not allowed to talk about Switch development outside the official developer forum.
First you need to register at and then apply via mail to nintendo to get the swith dev unit and get access to the switch forums.

There you will find info about how to get SDL2 for switch. And on that forum I and others can help you out.