I’m not a dev but there should be a content survey form for devs to fill out. Valve decided in this matter to not display games in Germany that have no USK-rating or if they don’t have a filled survey form. It’s about a law that enforces a age labeling.
Not sure if this link helps but valve has a page in it’s documentation about that https://partner.steamgames.com/doc/gettingstarted/contentsurvey/germany