I'm from Poland. Of course, everything depends on the conditions of the retirement that you're comfortable with. For me, it's 5000 PLN ($1300) a month till I'm 85 years old + paid-off house. The 5k PLN should be very comfortable assuming no children, which I don't want. Assuming ultra-safe investing to only protect the principal (i.e. no return above inflation) and wanting to retire at 40, you'd need around 2,500,000 PLN ($650,000) to achieve that + buy the house to retire in. Let's call in 3,000,000 PLN ($780k) in total.

If you look around a bit, as an in-demand (meaning - chasing the latest tech fads, maybe some tech lead experience as well) senior backend developer, you can get take home 250,000 PLN per year on a long-term (meaning usually multiple years) contract basis. Assuming 60,000 PLN of that goes to living expenses, it takes less than 16 years to save up the required 3m PLN to retire. And, if you're really hot in terms of CV, you can take home much more than 250k per year. Also, there are options to contract in Western Europe or get six figure remote US job (this one's harder than the other options) for more pay.