How to clean the Geberit wall drain shower in case of clogging?

Keep in mind that these were also the answers of a layperson, one with experience though, but it is still possible that your expert tells you something different. But then you can come again.

That’s okay ;) , the important thing for me was to understand where the crux lies. The product itself does not seem to be worse than the other processes. They all have the same problems with the narrow points of the pipes, etc. The accessibility is the main problem of the wall drain, that’s how I understood it.

I’ll find a store where one is installed, then I’ll get down on my knees to play around inside and decide spontaneously if it’s tolerable for me or if I’d be running into trouble again while romping around in the future :).
Step 2 is then to talk with the plumber about a sensible and effective pipe routing.

So thanks for this insight!

Yes, that's a good summary. At least in my eyes. One could also add that at least in my version, the entire chamber in the wall also acts as a dirt trap. How the sealing looks is also another topic. In my case, sealing slurry was used. I know that nowadays at least with the floor drain, a seal can be unfolded that basically works like sealing tape. You can also stick it well onto the floor around the drain. In the drain chamber of the wall drain, it is fiddly again.

Back to the initial question: Do you have a pressure washer? Then there is an accessory, a long thin hose with a nozzle that produces a strong water jet once forward and then multiple times backward, so that the hose pulls itself into the pipe and shoots away the dirt.