Yeah, Prussia was the stronghold against communism and fascism, moreso than any other part of Germany. It was also somewhat monarchist, with more than did so federally voting for the DVP, DNVP, and DDP.
Don't confuse elections with government.
The most important KPD strongholds - Berlin, the Ruhr and the Province of Saxony* - were all in the State of Prussia. As were many regions of particularly notable Nazi electoral success; pretty much all of East Elbia, Schleswig-Holstein, the rural Protestant parts of Hanover Province and so on.
What distinguished Prussian state politics was a powerful SPD leader - Otto Braun - who worked well with the Zentrum (who at state level were dominated by their sensible rather than idiot wing) and the DDP.
*Modern day Saxony-Anhalt, less Anhalt. More or less.