Which internet solution do you recommend?

Powerline networking is only sensible as an emergency solution when nothing else works and indeed has no place in new buildings. You will never get decent speeds... for your fakeHD Entertain that might still work... but with HD at proper bitrates and decent sound (Atmos etc.) you will enjoy a severely stuttering picture. And we’re not even talking about 4k yet... And it goes even further... with 8k, copper is also at its limit. We are installing an empty conduit in the living room to later get fiber optic into the living room.

And that is exactly the difference why for some (like me) Powerline is absolutely okay, but maybe not for others. My "HD Fake Entertain" is more than enough for my 42-inch TV, and my Powerline adapter easily handles the 50Mbit coming over my DSL connection. It goes up to 300, I’m also aware that it probably won’t fully reach that.

But if more bandwidth is ever needed, I’ll just buy other adapters – with a cable laid out, that’s difficult.

Another thought. I have a LAN socket installed in the child’s room, choosing the location to the best of my knowledge. Years later, the child gets a desk that is on exactly the other side of the room – LAN is tricky then; power sockets are usually on all sides of a room anyway.

But everyone will decide that for themselves – for us, it just wasn’t worth it.

Why Access Points instead of Repeaters?

A little problem with Access Points for us is the electrosmog. The topic is scientifically controversial, with studies going in all directions, but out of precaution, we would like to reduce this exposure.

The technician otherwise recommended 2 Access Points in the attic (pointing in opposite directions because they only transmit in a 180-degree radius).

And does the technician really know how the Access Points transmit??? How come???
And that no RF passes through drywall would be new to me.
Regarding electrosmog, you can just turn off the WLAN at night (I assume these are the bedrooms), since every reasonable Access Point allows you to set schedules. Do you not have any "radio devices" nearby otherwise?
In general, I would equip every room with CAT7 cables; what normally could go wrong with that? (I believe in France this is already mandatory!)
We have a Fritz!Box on each floor (there are others as well), but overall I think I installed 12 Cat cables.
WLAN for phones, iPads, etc. is available throughout the house (solid KS construction), and for example printers, TVs, etc. are hardwired.
BTW, fixed cabling is still the safest and least susceptible to interference.

Well, 8k streams already exist and have peaks over 50 MBit/s. Of course, compression is used but that's not a big deal. I don't think you have to see the end of copper right away. In-house cabling won't be a bottleneck for quite a while, if ever. For Dolby Atmos, you mainly need suspended ceilings and walls to be able to integrate the maximum number of speakers. Putting Atmos on 5.1, 7.1, or 9.1 is nice, but it misses the point. So copper cable is the least of the problems. Per LAN, per access point per floor.

But if there really should be more needed sometimes, I'll just buy other adapters - it gets difficult with a permanently installed cable

But the cable has at least 1,000 MBit... and as soon as you do more than just internet browsing and a bit of TV, you run into trouble. You can forget about a NAS with DLAN.

Another thought. I have a LAN socket installed in the child's room, choosing the location to the best of my knowledge. Years later, the child gets a desk that stands exactly on the opposite side of the room - difficult with LAN, since power outlets are usually on all sides of the room.

Then you are a bit flexible and lay a LAN cable behind the baseboard.

And that is exactly the difference why for some (like me) DLAN is absolutely okay, for others maybe not. My "HD Fake Entertain" is more than enough for me on my 42 inch TV, and my DLAN adapter easily manages the 50Mbit coming through my DSL line. It goes up to 300, I also know that it probably doesn't quite reach that.

Ok. Then you are simply the big exception of the people for whom even today an old Nokia is still enough (symbolically speaking... not personally!). Then you don’t need LAN, DLAN etc. for HD Fake Entertain even WLAN is enough.

Best regards, Micha

PS: 300 mbit over dlan??? come on... I’m almost falling off my chair! Measure it! My guess: 50-70 mbit!

You can forget about a NAS with DLAN.

No, you can also watch movies streamed from the NAS on the TV via PowerLAN and use the NAS for all sorts of other purposes, BTDT (in the old building). Be that as it may, in a new building I would not plan without LAN cabling.

In every living room:
2 x LAN
1 x TV multi-socket/SAT

That simply belongs to it, I wouldn't hesitate for long, the house is supposed to stand and be used safely for 50 to 100 years, also under changing circumstances (possibly changing residents).