...and your peak demand for energy is heating in the winter. Not convenient if you have to somehow store all that energy from summer for use in winter.

Though I guess Poland is still heated by NG, even if it’s coming from Russia. Heating with electricity is pretty inefficient.

Heating with electricity is plenty efficient if using heat pumps. In fact, a very high efficiency natural gas advanced combined cycle plant providing electricity to heat pump heaters with a COP of 2.5 or better (often 3 or more) is actually more energy efficient than burning the natural gas for heat directly, as crazy as that seems.

But yeah, finding clean sources of electricity in winter is a challenge for a place like Poland. Poor hydroelectric resource. Only modest geothermal potential. Modest solar (not good for winter load). But wind potential isn't too bad in the north of the country and in the Baltic Sea. Nuclear power should be considered, however, as it is in Finland.

I’ve never heard of heat pumps being used in say an apartment building that tend to dominate these sorts of locales, but perhaps that’s just because the technology is new and the buildings are old?

Nuclear has super high capital costs that usually must be subsidized by the state (and insurance definitely needs to be subsidized). Not to mention corruption has to be low enough that a disaster doesn’t occur. I can see less developed countries not being able to take this route.