[SOLVED] Question about region restriction

just your region would be the safest choice.

Since you are providing a key, the part with "cross-trading or gifting" isn't relevant. Germany is the only country where it can't be purchased and activated normally, so you could create a GA for all countries except Germany.

If you have key for the game, create a region-restricted giveaway for all countries except for Germany.

If you are planning to gift the game via Steam store, you can only gift it to the countries in your region, and if your region is EU, exclude Germany from the list. And if the country has a currency on Steam, you need to check that the price difference is not more than 10%.