TL;DR
Kant was born in what Ukraine and EU call Crimea but Russia now calls Kaliningrad; since Putin invaded in 2014 and illegally annexed that part of Ukraine.
Putin has a real obsession with not being European enough. so his point of (mis)quoting Kant is about trying to prove that Kant wasn't really German, nor European; but Russian. that area + Poland were part of the historical German Prussia.
Scholz sees it as Putin's threat to eventually claim Germany & Poland as Russian too.