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Hard to believe but seems to be a shrub of the genus Chaenomeles...

Could be so, even if i wouldn't expect that species growing in the wilderness of the polish (mainly pine) forest.

According to https://www.researchgate.net/publication/319665331_Chaenomeles_-_health_promoting_benefits
some species can be found in Poland.
I'm not a 100% sure but this is my guess also: Chaenomeles. Which one...hard to say without a flower or a ripe fruit.