IMHO, Ukrainians should grab Königsberg for themselves after the end of war and then exchange it for something useful, e.g. exchange it for Transnistria with Moldova, instead of returning Königsberg to Germany.
Why we need to try exchange Transnistria for Konigsberg in the first place?
https://en.wikipedia.org/wiki/Russian_military_presence_in_T...
And then? You have a piece of territory that is ethnically and culturally Russian, but integrated into Europe instead of that whole "Russian World" nonsense. That can be used as an agitprop showcase to contrast with Russia proper, especially as things get worse there as economy starts feeling more long-term effects from sanctions.