Sure, a common use of bread, potatoes, cabbage/other vegetables, hearty meat dishes etc but the Polish kitchen is closer to Ukrainian/Russian in technique/ingredients.
Barszcz, pierogi, fermented everything, pickles, sour rye, and many dishes built around wheat/rye, mushrooms, dairy, and Eastern-style fillings are much more like Ukrainian/Belarusian/Russian food.
The biggest German influences are probably the sausages and the beer culture.
How reasonably can German cuisine be described as a single unified thing? My mother was from East Prussia and my father from Swabia and their "home" cuisines were pretty dissimilar -- if for no other reason than climate.
It's also true for Belarus, Baltics, and some parts of Ukraine. Generally, we can speak about North-Eastern European cuisine with potatoes, secale flour breads, and various pickled things. And that name will make a lot of everybody upset, cause everybody in those lands pretend they are "Central". Americans would not believe how many "geographical centers of Europe" are claimed there.
I'm not sure how surprised Americans would be to learn that there are so many "centers of Europe". After all, we all know that Colorado is in "the west", Texas in the "southwest", and, clearly, "the South" is located in the geographical southeast :D
Due to Partitions of Poland a lot of of territory was under Prussian influence for over a century - that had to have some culinary effect (other than forced germanization).
Barszcz, pierogi, fermented everything, pickles, sour rye, and many dishes built around wheat/rye, mushrooms, dairy, and Eastern-style fillings are much more like Ukrainian/Belarusian/Russian food.
The biggest German influences are probably the sausages and the beer culture.