Use Trade In in Germany for iPhone Purchase in the USA

iPhone warranty is NOT international. Why would you want an iPhone from the US if you live in Germany? There are also regional difference in iPhone's sold around the world. For example ALL iPhones sold in the US are dual eSim only. Does your carrier in Germany support eSim? There is no physical SIM in any iPhone sold in the US. Will you be OK if you need warranty support on your iPhone in Germany and need to hop on a plane and fly to the US to get service?

It is ALWAYS best to buy your iPhone where you live and will use it.

no

No for the process mentioned in your post.

You trade-in and take a Store Credit and use the store credit to make a purchase. They will send you an Apple Store Gift Card via email.

The American phone will have no warranty in Germany and the 5G cellular may not work

...and if you don't declare it and pay the import duty and VAT it is called smuggling.

Still looks a bargain?

You're welcome, additional information that it's a very bad idea all round.