This jam is only for "retro style graphics" games or also actual NES/Atari 2600/... are accepted (as long as they run also on browser)?

Can you clarify? Do you mean an actual existing NES/Atari game, or do just mean one that looks like Atari or NES? Or are you meaning taking something you made for an emulator that runs on NES/Atari?

I mean a new game made specifically for the jam in assembly for an actual retro console. The game then could be played in browser or downloaded to play on emulator or real retro hardware.

yes, as long as jam participants can play the game.