Which smart home system is suitable for our new building?

Thank you, I was just uncertain because everyone always talks about Unifi Access Points being much better than those from AVM

Then just buy the Access Points from Unifi. There is absolutely nothing against a mixed operation of different manufacturers. I can't answer details about APs, I have neither Unifi nor AVM APs.

I just want good Wi-Fi everywhere, and it should support IPTV, surfing, and gaming

Just look for your desired hardware and check on Google whether your IPTV solution works with the devices. What kind of IPTV do you want to use? IPTV is not the same as streaming like Prime and others. Gaming only via cable.

The Fritzbox has to be placed in the basement because the modem is needed there. Or would you use the standard modem from the provider?

No, you can put the Fritzbox wherever you want. See my example. The TAE socket for my DSL connection is located in the basement next to the 19" rack. From the socket, I go via an Ethernet cable directly to the Fritzbox in the living room, and from the Fritzbox via a second cable back to the basement to distribute everything further. If you can’t name a technical reason against the provider’s standard modem, why would you want to replace it?

Man oh man, now I'm writing again.

But maybe as a hint to everyone else: It doesn't matter at all what you write here. If he reads it, he doesn't understand it and asks exactly the same thing three pages later or in another thread under his other accounts again.

The Fritzbox has to be placed in the basement because the modem is needed in the basement
Or would you take the provider's standard modem?

I had already answered that a few pages before, for example:
https://www.hausbau-forum.de/threads/welches-smarthome-system-fuer-unseren-neubau.43819/page-23#post-588078

It is hopeless here.

I don't yet know exactly what we will get in the basement whether there is only the fiber optic cable connection or already the modem from Vodafone

It is important to me that I only have 1 mesh (possibly wrong term) WLAN, meaning 1 login and I have WLAN everywhere and the device automatically connects to the access point with the best reception that only works if you stay with one manufacturer

What still holds me back from Unifi are the high costs with Unifi you should take all components from Unifi (router, switch, access point)

especially the switch is extremely expensive 16 port POE 250€ (even 400€ with 19 rack mounting) a normal 16 port switch costs about 75€

the access points Unifi Mesh6 also cost about 220-250€ each Dream Router about 250€

that only works if you stick to one manufacturer

Who says that? You can certainly use APs from different manufacturers at the same time. Same SSID, same password, and your device will automatically connect to the strongest network.

KNX way too expensive and overrated. Rademacher Homepilot controls shutters, door contacts, smoke detectors, shutters opening in emergencies, Hue lamps, heating at the lowest cost. Everything perfect.

Knx way too expensive and overrated. Rademacher Homepilot controls shutters, door contacts, smoke detectors, shutters in emergencies, Hue lights, heating at the cheapest price. Everything is fine.

It doesn’t look that promising, okay for retrofitting, e.g. rental apartment, but if I build new, then not a system that only relies on wireless. Then you should use something a bit more professional.