The Germans have specifically ruled out doing East Prussia again, for the same reason a recovering alcoholic won’t touch a drop of wine. Which leaves two options: Králiveč, the Czech exclave with a beer pipeline to the mainland*, or the more mundane option of partitioning it somehow between Poland and Lithuania.
* which should probably be named in honour of Immanuel Kant, a famous local reputed to have been a real pissant who was very rarely stable
Germans are still suffering from having to integrate another failed quasi-soviet state more than 30 years later, so you couldn't pay them enough for taking Königsberg back.
Though having instantly given citizenship to thousands of Russians on the grounds that their ancestors around the time of Catherine the Great were German, and ending up with a monolingually Russophone voting bloc that gets its news from Russian state TV, did them no favours either. Jus sanguinis: not even once.
Wait, we germans take königsberg back and throw the russians out and just make it a nice patch of land for bavarians. We gain a beautiful countryside in mainland germany and könich maggus can have königsberg to make average bavarian things
However, it would be somewhat entertaining to see the AfD melting down over getting it back. On the one hand, you have some of the old territory back, but on the other hand, there's so many foreigners getting your nationality now…
Given that AfD are Putinists and a significant proportion of the foreigners are Russian military personnel, I suspect they wouldn’t have a huge problem with it.