I agree with TFA. Probably the best value for the buck is a 3 year old high-end Thinkpad (T or X series); you can often find one for €250-350, as many businesses will be replacing whatever is at the end of their 3 year cycle.
I've been getting a new one roughly every 3-5 years and they definitely stay good enough for another 5. My latest score is a T495 (replacing an 11 (!) year old X230); it has 4 cores (8 threads), 24GB of memory, two NVMe drives, 4-5 hours of battery (~270 cycles), full HD 400 nits screen, and a GPU that actually handles some games. It's definitely less powerful than my M1 Mac mini, but it's good enough to the point that I'm not missing the extra horsepower all that much, even when doing "Actual Work" (it can get tad hot tho).
Also, developing software on less powerful hardware has another, indirect benefit: your software tends to suck less, because you have less cycles to waste.
I've been getting a new one roughly every 3-5 years and they definitely stay good enough for another 5. My latest score is a T495 (replacing an 11 (!) year old X230); it has 4 cores (8 threads), 24GB of memory, two NVMe drives, 4-5 hours of battery (~270 cycles), full HD 400 nits screen, and a GPU that actually handles some games. It's definitely less powerful than my M1 Mac mini, but it's good enough to the point that I'm not missing the extra horsepower all that much, even when doing "Actual Work" (it can get tad hot tho).
Also, developing software on less powerful hardware has another, indirect benefit: your software tends to suck less, because you have less cycles to waste.