Poland saw net increase of GDP by 1-2% solely due to immigrants in 2023. And that number is from their own Warsaw institute, not some outside entity. In the same time period Poland saw immense monetary inflow from immigrants, who had to spend their money in the country, far more than any spending on those same immigrants.

And this is super short term data. Imagine how much better they are in long term, after assimilating and finding good jobs, founding businesses etc. Poland was losing population and in general not topping development charts, but immigrants fill this gap and boost the economy.

PS: an anecdote - I'm now an adult immigrant in Poland. I'm paying approximately 39.5% of tax now, a crazy rent to the Polish citizen landlord and all local products and services. I won't be eligible for Polish pension for two more decades, and after that I'll probably get some minimal one because I've started too late. I'm also paying some incredible sum to the healthcare system (included in those 39.5%) while not using it much. Statistically the most ill human groups are kids and elderly. Immigrants skip the kids stage themselves and elderly part is very far into future, so they are net gain in the healthcare system.