Minimum wages in Poland were 610.79 EUR/Month in the first half of 2020.
https://tradingeconomics.com/poland/minimum-wages
So a average single mom with one child, which earns 610.79 € per month will get no child benefit, as the limit for the first child is 182 € per capita (610.79 € : 2 heads (mom + child) = 305.395 €).
So the law does exactly, what my linked article is claiming:
Sorry, one more neocon lie exposed.single parents with only one child need to be means- tested in order to receive the benefit. That particularly hits single parents, as it is them who are likely to have only one child. One- third of all children in Poland are brought up in one parent families. Considering that the number of single mothers in the country is eleven times bigger than that of single fathers, the restriction on child benefit is particularly hitting the women who, one may think, deserve particular care from the state. Single parent families however do not fit the right- wing government ideal of the family, so they are not supported.