New single-family house in southern Germany

If I have concrete problems with the layout, just bring them up.

Technically no, "at most" some with aesthetics. Decorating the driveway with a Frankensteinian "archway of horror" composition is very, very a matter of taste. A house shared with a woman is well advised to visibly leave the wild bachelor-den years behind. Your "layout" looks like socks lying around.

A proper staircase leading up would of course also have its advantages to really use the attic. Carrying an old armchair through the hatch is certainly no fun you would want to do often.

......when planning a new residential house such a thought would be rather foreign to me.....an old armchair in the attic? What else is coming? You already have a garage arsenal.......
Maybe the knot that should be untied also lies in this area.

an old armchair in the attic? What else is coming?

I read somewhere: ...for things you no longer need but don't want to throw away“. For that, there is honestly eBay... you don't build a house to store things you no longer need. That is post-war thinking.

......when planning a new house, such a thought would be rather foreign to me.....an old armchair in the attic? What else is coming? You already have an arsenal of garages....... Maybe the knot that needs to be untied lies in this area as well.

A garage is for the car. With 6m external length, there’s no space left for junk either. And can’t anyone really understand that for a building I will be paying off for 20 years, I don’t want to end up without proper storage space? There are plenty of things you sometimes need and don’t want to have lying around in the living space: camping equipment, ski gear in the summer, sailing gear in the winter half of the year, and so on. And honestly, what do you get for a used armchair? In the countryside, you’d be lucky if someone comes to pick it up for free.

A garage is for the car. With 6m external length, there’s no room left for junk.

Building is expensive, every square meter costs. Therefore, planning makes sense. One should define "junk" for oneself and consider whether the additional space created for it is more expensive than the "junk" itself. That’s why I don’t really have such stuff.

And can no one really understand that when I build something I will pay off for 20 years, in the end I don’t want to be left without proper storage space?

Yes, absolutely. Storage space is important. But it’s just as flexible a term as wardrobe. For some, 2m is enough; others prefer to collect and have 8m. Your "old armchair" in the attic caught my attention. An armchair is used, and if no longer, then it gets removed. I buy used/valuable furniture that I will not give away again. I will not have an "armchair storage room." Collecting is an expensive hobby in a new build, but yes, sensible storage space in/around the house is an extremely important point. What I can, I store in the garden house, carport, or similar; it’s cheaper there.

And honestly, what do you get for a used armchair? In the countryside you’d be lucky if someone comes to pick it up for free.

Use it or give it away, then buy lasting quality, and the problem is solved once and for all.

I know, space in the house is expensive. But outside is also difficult. A garden shed with 40 cubic meters fills up quickly; roughly estimated, I can divide it about half for bicycles, lawnmower, and garden tools, and the other half for a small workshop. Garden furniture in winter will then be a bit of Tetris again. A second garden shed would be allowed, but it would then stand right in the middle of the garden since with a 6m garage and 3*6 garden shed I have already used up the 15m boundary length. And then a 700sqm plot gets built up very quickly. Ergo, proper storage space inside the house is also necessary.
One could, of course, still optimize the boundary construction with an 8m garage that also fits bicycles and a 3*4 garden shed. But the garage then becomes quite massive and the house shifts far to the west. So not exactly a really great solution either.
By the way, the thing with the armchair is not just an example made up out of thin air. I have one here (a bit worn but otherwise still great) which is now going to my parents for Christmas and will be stored there at first because we need the space in the living room corner for the baby cradle. In such cases, I am always glad that my parents built a garage with an attic back then, even though everyone advised against it. The space is simply unbeatable.