I got a huge question: I bought Divinity Original Sin Enhanced Edition for a friend on GoG. But my Graphic card can't support DirectX11 on Steam. So im thinking im just going to play the vanilla version which i have on Steam, but I don't see anywhere on GoG to download the vanilla version without the Enhanced Edition.

If you didn't get the GOG version of D:OS before the EE was released, I don't think there is any way to get it now.

For Steam, the Humble Store still has D:OS keys, and any retail released of the game still around are Steam, but it can not be bought directly.