What are the experiences with recirculating range hoods in new constructions meeting KFW40 standards?

It is also particularly about the exchange of possibly humid air ... cooking pasta, etc.

But you said that nicely! Most people just want to get rid of the "smell when cooking."

Fortunately, I don't know many things and therefore I don't miss them.

cross out “therefore”, replace with “because”

If frying is done regularly and occasionally even frying in deep fat, the cheap convection is not sufficient.

Insufficient for what? It depends on what you want to achieve.

(I write this because the argument "you don't miss what you don't know" is not a good one. If it were, you wouldn't be able to know what you need...)

Yes, exactly that is it: Good! "You don't miss what you don't know" is fundamentally vital for the individual’s survival. Of course, this does not apply in consumer society, where people boredly Google Amazon, Tchibo, and Temu up and down to see what else they might need. Who likes that?! I also went through this phase for a short time – ultimately nothing stayed in the household but was given away, sold, ended up in the trash or at work. Things you don't need, but think you need.
This also applies to kitchen purchases or specifications: some specify and want everything, often many things twice in one kitchen, as if it cost nothing. But I won’t go into details here. Everyone has to decide for themselves what to spend their money on. The OP at least seems to be thinking about WHAT he needs and not what he could need just because others think they might need it.

Right. And my recommendation is to name the use case.

Yes, I actually miss that here again and again in threads, whether everything could fit everyone. Yet it is precisely the individuality of the user that makes the real difference. If something bothers me or is important for my well-being, then the price takes a back seat and I buy the best-suited option because otherwise, I would feel uncomfortable with it.

For a steam oven/kitchen where nothing is fried and things are rather grilled on the balcony, standard convection is enough.

We do cook (live) indeed, but very little fried food and if so... grill. In addition, there are no more kids running around here with a need for fish sticks...

If you sear sharply inside the house, fry green herrings for pickling, 3 kg of meatballs for buffets, or make large amounts of fried potatoes on a hot iron (those are very odor-intensive messes for us), you simply need a different solution. And then I advise exhaust air or very high-quality convection variants.

I will find your address; if you tell me the time now, I will gladly come by once to check your extractor hood... while I check the quality of these culinary messes.

I understand you exactly, I generally prefer fewer things, but mostly the "better" ones. If I had such a cooking passion, my text would be completely different. I think you know what I mean.

I see in some kitchens the suspects mentioned here (Bora etc.) but often not the "associated" enthusiasm for cooking; sometimes this is even rather weakly pronounced. When I then try to understand that someone installs such a thing maybe even only for reasons of appearance or design, I can also comprehend that... why not. What I cannot comprehend, however, is that in the same house someone sits on a completely low-quality sofa or only random ready-made pictures from the furniture market hang on the wall. What I miss then is the broad and understandable desire for quality for oneself (after all, one also sits a lot and likes to sit well) or other beautiful or lovingly designed things in the house. Sometimes I almost get shocked when I see such a discrepancy. A Bentley in the kitchen and plastic covers from KIK market in the Bentley. I do believe that currently the kitchen topic serves a disproportionate trend in new builds, which does not match broadly with cooking behavior. In this respect your remark fully applies:

Right. And my recommendation is to name the use case.

... even if it is simply supposed to look chic or crazy. Unfortunately, I only read:

We would like to install a recirculation extractor Bora, Neff or something similar.

... and no necessary reasoning why one has come to this intention (technology, performance, need, appearance.....) So - probably the OP will now just take an extra tilt window......

I am a fan of exhaust air, I admit.

... as long as that is the only fetish

We often also have pots or Sugos simmering, which give off steam for hours.

I also see the use case "exhaust air" or the increased demand here. And whoever plans a house newly and considers exhaust air can also include a supply air solution specifically for this use case in the planning. Weibel supply air boxes. This saves opening the window with often uncontrolled and unpleasant drafts and supplies fresh air purposefully for the exhaust air. Odors cannot be avoided with any extractor fan solution. After all, the food does not move from the cooktop into a hermetically sealed container but to the table to be eaten together. And the food does not stop smelling then. In most cases, this should rather be a pleasant smell.

What I do not understand, however, is that one sits on a completely low-quality sofa in the same house or just hangs any ready-made pictures from the furniture market on the wall.

I see it the same way ..

This also applies to buying or sampling a kitchen: some sample and want everything

... and forget to pay attention to ergonomic arrangement and workflows. And then in the end it is not used as originally thought.

But yes, that's exactly it: Good! "You don't miss what you don't know" is fundamentally vital for an individual's survival. Of course, this doesn't apply in consumer society, where Amazon, Tchibo, and Temu are googled up and down out of boredom to see what else one might need. Who likes that?! I also went through that phase briefly once – in the end, nothing remained in the household but was given away, sold, ended up in the trash, or at work. Things you don't need but think you do.

Hm... I meant it literally, not related to mental stability. People also don't miss medications they don't know about, but instead cope with the consequences of illnesses if they have to.
That you know what you really need stems from your experience with things you wanted but turned out to be useless. So because you know them, not because you don't.
Otherwise, I agree with your description of superfluous consumption.

What I miss is the broad and understandable desire for quality for oneself (after all, one also sits a lot and likes to sit well) or other beautiful or lovingly designed things in the house. I sometimes almost get shocked when I see such a discrepancy.

With us, this desire for an aesthetic that corresponds to our taste runs through everything. But first, you need to have a taste. I know very likable people who don't have one. None at all. But they don't miss anything either and are satisfied – totally okay. Just not transferable to, for example, me.

I very much like to take a look at your extractor hood once... while I check the quality of these culinary atrocities.

Unlike the food, the hood is very inexpensive. Exhaust air on a 200 mm pipe doesn't require technology above a small standard, as the pipe is the bottleneck with smaller diameters. We took over my parents' 17-year-old hood along with the kitchen. We ventilate our split-level house from top to bottom using the hood when we want. Today, I would invest money in noise reduction.

That you know what you really need stems from your experience with things you wanted but turned out to be useless. So, because you know them, not because you don’t.

That is often just the consequence of that.

People also don’t miss medications they don’t know about, but rather cope with the consequences of illnesses if they have to.

I mean it just like you do – you cope with a condition/problem etc. if you don’t know anything else. However, I wouldn’t call that coping, because you don’t question it or critically oppose it. Look how happy we all were before globalization. Nobody knew about smart homes and was satisfied with their light switch. When we built, we have already been living in our house for over 10 years, this forum existed back then, but certain devices were only installed in correspondingly high-quality kitchens in kitchen studios. Which I didn’t even look at. I don’t even know if those holes in the island already existed, but recirculation built into a “lamp.” We have a perfectly normal recirculation hood, like all in the neighborhood – it does what it’s supposed to do. I have never seen Berbel, Bora, and co. in action, so I don’t miss them. I turn on my Franke and that’s it. If it bothers me, off. I don’t question it, and I don’t question whether I would be happier with a new different one. If there is mentally a new kitchen coming, I know about 1-2 features that have to be. The exhaust/recirculation concept is not among them. Insofar the sentence is good in my eyes, because my need is covered and that makes me happy. I lack nothing because I don’t know it.

I write that because the argument "you don’t miss what you don’t know" is not a good one. If it were, you couldn’t know what you need either...