After the climate change activist Greta Thunberg testified at the United Nations, urging world leaders to take action, the presenters on Polish state television said viewers needed some context.

They displayed a photograph of Ms. Thunberg standing with George Soros, the billionaire investor and progressive political donor. They said it is evidence she belongs to a supposed global cabal that opposes the nationalist ruling party in Poland, Law and Justice, and populists around the world.

But the photo was a fake. Spread widely online by far-right extremists, it combined the head of Mr. Soros with the body of Al Gore, the former vice president of the United States.

It was just one example of how much the state media has been turned into the mouthpiece of Poland’s government, raising concerns about how fair the country’s elections on Sunday can be and eliciting objections from European Union officials worried about media freedom.