Like carve out a place between Russia, Belarus and Ukraine in the former Pale of Settlement. Establish a bunch of Yiddish language schools there. Have it become a center of Jewish culture. Sure, there are already Ukrainians, Russians and Belorussians there but there were already people in the far east too.
They totally should have given East Prussia to the Jewish state instead of settling it with ethnic Russians while supporting the creation of Israel and making the Jewish Autonomous Oblast.
The totally should have made eastern Germany a Jewish state instead of settling it with Poles who had very little prior presence there. Prussia too ofc.