I recently saw Anno 2070 on sale on steam and was surprised not to see the in library tag on it as I remember buying it in a sale, and I remember playing it. I am going to send a message to support but is there anything I could be missing.
Did you buy it on Uplay? Or maybe you're looking at a bundle which has the game plus DLC - if you fin the store page for the game on it's on does it show up? I'm assuming you've searched your games library for Anno?