Separating the knee wall from the living space, what is durable?

Friemelig ist es nur die Bretter genau passende für jede Lücke zuzuschneiden.

Only if you want to fit them into the panels - I would rather choose "rahmenüberdeckend".

Of course, you can also equip the panels with hinges or piano hinges, but I actually find the option with magnets much easier. I am still looking for a disadvantage

Are there still spiders living back there?!? It must be airtight ...

Well, that's a different topic anyway. Personally, I wouldn't want to store anything back there because it's not really sealed at the back. But if you then build suitable cabinets at the back, it either becomes 1. quite complicated or 2. really expensive if you have it done.

What would bother me about the magnet solution is that I would always have the board in my hand and would have to put it down first; I would rather use hinges. But in the end, it doesn't matter and is a matter of taste.

Are there still spiders living back there?!? It must be airtight ...

Personally, I wouldn't want to store anything back there; it's not really sealed at the back.

Why should it not be sealed there? The paneling, meaning the interior design of the slope, runs continuously down to the floor. For practical reasons, a KS was installed here. Apparently a heated room that one wants to use with boxes instead of a shelf. I would do it exactly like that.

Are there still spiders living behind there?!? That must be completely airtight ...

Actually creating this completely airtight room should hardly be possible and in my opinion not desirable either. Spiders and similar creatures are everywhere in the house anyway, where no space is absolutely airtight, depending on its location/environment. Only creatures that are already in the house can get in somewhere. Basically, it's like a storage room or something similar, where you can always check what’s going on behind the stored boxes; just like on or inside the wardrobe, which is also deliberately not airtight. Depending on craftsmanship skills or available craftsmen, you can build this properly and cheaply in various ways as shown.