Are LAN sockets still up-to-date? WLAN/wireless is the future!

No, Steffen, having several APs does not necessarily mean that. Most people have no idea and do not deal with transmit power, channels, and frequency bands... Mesh systems are now usable. However, they have no place in a new building because they are a crutch solution (e.g., retrofit). Fundamental discussions have already been held here many times. One person is fine with a can-do-everything-but-nothing-right box from the provider for the whole house, and another needs good 5GHz coverage everywhere, everything on cables that is possible, and also a 10Gb network... The fact is that currently there is no WiFi that even with only one client directly next to the access point has the speed of 1Gbit Ethernet. When more clients are added, it gets even worse.

Of course, it is always the question of which device needs what. I wouldn't necessarily connect the backup server to the Wi-Fi either, and the multimedia box on the TV (or such a modern SmartTV ;)) certainly makes sense on the cable as well. But for most devices, speed is not that relevant. Besides, Gigabit doesn't bring much behind a DSL 50 000 either.

It depends on what you do in your network. You can no longer fully utilize a 1Gbit connection with Wifi (at an Accesspoint). Many things are also accessed locally. As mentioned, it also depends on your own requirements. I also have separate networks for different applications. For most people, a guest network is more of an exception...

Simply more access points :) which is by no means wrong if it solves the problem.

Yes and no. In the expansion stage like with , you should definitely know what you are doing, otherwise the many APs will only make things worse. You shouldn't forget that in Germany, even in the popular 5 GHz band at 80 MHz channel width, there are only four separately usable ranges, of which at least one, and sometimes even two, are usually blocked by DFS. If you want 160 MHz channel width, there are only two left, one of which might also be lost.

I thought the problem with drywall was the metal stud frame, which acts like a Faraday cage.
I didn’t think that bound water was also an issue...

I was at a fire test in December where gypsum boards were used. After a certain time, dripping started on the fire-shielded side in some places. If you didn’t see this, you wouldn’t believe it. You also have the metal stud frame, of course.

The more access points you install, the lower you can set the power or should even reduce the power of the access point so that the networks don’t overlap too much. From my point of view, this results in less radiation exposure.

One person is satisfied with a can-do-everything-but-nothing-right box from the provider for the whole house, and another needs good 5GHz coverage everywhere, everything possible wired, and even a 10Gb network...

You have probably mentioned it somewhere before, but have you actually implemented 10GbE LAN now? If the hardware weren't so expensive, I would find it a cool thing even for the 'heavy-duty' devices in the network.