Which smart home system is suitable for our new building?

not yet exactly
I have the following devices in mind:

with POE: TP-Link Omada or Unifi

without POE: AVM

what I didn’t understand about the AVM repeaters is that they advertise having a great MESH system

I am interested in the Repeater 6000 or the Repeater 1200 AX

what I didn’t clearly understand are the LAN ports on the repeaters, output only? or are they for connecting the repeater to the LAN?
I definitely want my repeaters/access points to be connected to the LAN and not receive and then amplify the WLAN (wireless signal)

What is being made a big deal of here are ridiculous power consumptions from ridiculously few devices…

and small switches (only if needed) powered with PoE so that I need one less power outlet in the rooms
No devices requiring PoE would be connected to the small PoE switch in the rooms

Works perfectly, saves one power outlet. I had exactly that in my penultimate apartment as well. But there it was an emergency solution because it wasn’t my apartment and there were too few LAN ports in various places. In new buildings, however, as said, it’s a compromise, but a viable one.

Would it make sense to control the access points via normal LAN cables, then connect them to a power outlet that goes directly to a KNX binary actuator in the basement? Then you could safely turn the (Unifi) access points off and on at a certain time (if you don’t want to deal with the WLAN radiation)

Is your house fully and effectively shielded against radiation from outside and do you switch off all mobile devices and other wifi devices completely at night?
Only if you answer both with yes does it make somewhat sense to think about turning off access points.

Thanks for your answer.

Which devices do we need for our network?

We have 12 LAN ports in the house and will install a maximum of 4 POE access points (the WALL APs always have an integrated switch with at least 1 POE out and then 1-3 regular ports; on the POE out of the access point I would only connect a small 4-port POE switch if necessary (which is very unlikely))

Which devices would you recommend to me?

Unifi, Omada (or others) or just AVM (without POE then)

Unifi 16 Port PoE Switch, suitable Unifi Access Points and the controller on a Pi or NAS. Note that some Access Points only pass on passive PoE.

May I ask what Unifi does better than Omada? Unifi is already quite a bit more expensive than Omada

No idea, you wanted a recommendation, here it is. Unifi just works and I have extensive experience with it. Not with Omada. You can easily integrate Unifi into various building controls if you want.