Control of multiple roller shutters

Very simple reason: I wouldn’t want to squeeze an actuator into every wall socket and light switch box. This is much more elegant with KNX, and laying the cables is less complicated than the (subsequent) installation of the actuators. In addition, there is a much wider selection of actuators, sensors, and switches with KNX. With wireless systems, you always have to make sure that actuator A and switch B are actually compatible with the gateway installed at home.

Furthermore, with wired sensors (motion detectors, humidity sensors, etc.), you don’t have to change the batteries all the time (Enocean motion detectors, for example, unfortunately have batteries). With small projects, this is no problem, but if your entire house is full of them, it quickly becomes annoying.

I would never think of using a wireless solution in a new building. You never know if it will really work. Especially since the mentioned requirement can be easily fulfilled conventionally. It doesn’t get more robust than that.

Yes, you can also exaggerate everything to excess. I have so much on the oh-so-overloaded frequency band. Where is the problem? The switch is not streaming a movie or gaming online. The data it sends over there is ridiculous. And for a few blinds then install KNX. For me, that is totally off topic and pure money burning. I don’t know how much cash you took out for your house, but KNX is not a cheap alternative. There is plenty of cheap awesome stuff over 2.4 GHz WiFi that doesn’t affect the frequency at all. As I said, you can exaggerate everything.

But even there, control is done in the meantime via KNX only, and automated via e.g. openHab, as it is significantly more flexible.

Not really... only people who don't really know what they're doing do that. KNX forms a backbone in a "proper" installation including as many automations as possible on the application level (as a fallback). And only then do additional solutions come on top, so to speak.

There is a lot of cheap cool stuff over 2.4 GHz WiFi that the frequency doesn't affect at all.

With installations above a certain size, definitely yes and quite noticeably. Just because you haven't encountered the limits yet doesn't mean they don't exist.

From a certain size of the installation, definitely yes and quite significantly. Just because you haven't encountered the limits yet doesn't mean they don't exist.

Yes, but where is the limit?

I will also rely on Shellys and am currently testing them in my rental apartment. There, I receive over 20 WiFis from the neighborhood and I have no wireless issues with the Shellys. With a cheap router through reinforced concrete, I have a connection. Should the connection ever drop, they of course also work without a WiFi connection.

The limits are individual. In a concrete bunker, they are reached faster than in a timber frame building, and even a microwave or WLAN cameras (which are also popular with the same radio installations) can significantly interfere with the operation.

Why one should rely on radio in new buildings is equally incomprehensible to me. Provided, of course, one wants an automated house and not a playhouse.