Semi-detached new build, which technology to install?

As long as you do not use systems with closed source / cloud-based connections, you will be able to implement meaningful automation and comfort options with them over a long period of time.

Why shouldn't you use them? For example, that would be the case with Homematic ip, or am I misunderstanding something again?

why shouldn't one use them? That would be the case with Homematic ip, for example, or am I misunderstanding something again?

probably expressed wrongly: I meant systems with their own central unit through which the communication runs. Something like: Everything only works with this one main device. For me, only open wireless standards are acceptable, where one can hope that they will still be supported in 10-20 years. This is the main argument of the KNX faction – "never bind yourself to just one manufacturer," right?

So Openhab already sounds very good. How can I implement that with the Raspberry, sounds a bit complicated.

As I said, in my current apartment I have various Alexa devices (including Echo Plus), Philips Hue products, devices on Osram wireless sockets, and Xiaomi products.
Everything controllable via Alexa, but of course several apps.
In the new house, all of this should naturally become a bit more comfortable.
If I now decide, for example, on new products (roller shutter control, etc.) for Homematic, I can control everything together via Openhab, right? However, I would then need either the Access or the ccu3, right? That would then be one more device and app again. And basically, they are again different products (standards) for the various devices.
I just don't know what I should decide on. I don't want various different devices, but of course I also don't want to be tied to one provider.
So maybe once again my request on how I can implement the whole project a bit more smoothly.
Many thanks.

So Openhab sounds really good. How can I implement that with the Raspberry, sounds a bit complicated.

If the implementation on the Pi sounds complicated to you, OpenHAB will pose even bigger challenges. If you are open to DIY systems based on Pi, take a look at ioBroker. With your knowledge, you will probably get much faster usable results there. But be prepared that you will have a new hobby until something halfway usable comes out, no matter what you choose. Whether all your IoT gadgets can be sensibly integrated, you have to check the adapter or compatibility lists of the control systems. I have someone in my circle of acquaintances who has built his entire house with Homematic IP. That seems to work quite well for him, at least he only reports positive things to me. If you already go down the DIY route, that is probably something reasonably clean for a new building. Building a new house on Osram wireless sockets, Xiaomi stuff, and Hue bulbs, I consider the completely wrong solution. You can do that if you live in a rental apartment and cannot change anything about the electrical system.

I consider building a new system based on Osram smart plugs, Xiaomi stuff, and Hue bulbs to be the completely wrong solution. You can do that if you live in a rental apartment and absolutely cannot change the electrical wiring.

That's exactly the current situation I am happy to deal with new things in a new build. In addition, of course, it would be great if I could somehow integrate the previous things as well OpenHab didn't sound that complicated at all. And I'm not technically clueless, but I am neither an electrician nor an IT specialist and therefore a bit uncertain

As I said, have a look at ioBroker. For me, it is currently the most appealing solution for such problems. Especially since you can easily cobble together automations with Blockly. Check out the videos by Matthias Kleine on YouTube about ioBroker (Haus-Automatisierung). You should be able to quickly see if you feel confident enough to do it.

I find OpenHAB somehow too rigid. If you can really program well, it can be a powerful tool. Until then, however, in 99% of cases it is rather frustrating.