Is the neighbor's ventilation system set too high and therefore too loud?

Nice that help could be given ...

writes me a letter saying I should ventilate but with a lower volume flow.... I wouldn’t know if I would react as coolly as your neighbor apparently does.

That is not written in the letter...

I would still be interested in the new development area or residential area where one can measure 35db during the day in Germany?

I would like to know that too. I was just sitting on the toilet, you can't hear anything except me, and if I'm not doing anything except breathing, it's 36 dB. Oh, by the way, phone mics are not exactly great for something like this. So it might be that there is actually a higher sound pressure in some frequency ranges (e.g. below 100 Hz). The phone mic just doesn't measure well there, and low frequencies carry further....

I would still be interested in the new development or residential area where you can measure 35db during the day in Germany?

Answer for the gold scale ;) : on my terrace at 8:59 pm there are just under 40 db(A). At 9:01 pm (when the controlled residential ventilation is off): 35 db(A). All with no wind, no cars passing by. Birds are also quiet sometimes etc. Yes, these moments exist.

As written, amateurishly with the mobile phone.

Thanks again for the constructive contributions. Topic closed for me.