Hmmm, I'm just guessing that they probably didn't do that age verification thing they need to do to be able to sell in Germany.
I didn't find any indication on Steamdb that it won't activate anywhere, but maybe I'm just hoping :)

You can check the game out on it's official site or maybe on steamdb.

I can see the game in the Steam store and I'm from Germany

could be a unity game
lots of them have been removed from the steam store until they update and fix the huge vulnerability that was recently found out about

No problem, sometimes a little bit of AFK time is what we all need, enjoy the game when you get to it :)