Is building a basement still justified today?

Depending on the garage, it's quickly 10-20,000 euros. A pure utility basement has a price per square meter of under 600 euros (if it is not WU).

For a built-up area of 100 m², the basement therefore costs about 60,000 euros (roughly).

I am not sure if I am meant here, so I will answer anyway: It is indeed planned that two cars will be parked in our double garage and that the garage will NOT be misused as a storage room. Therefore, in addition to the 6 x 6 m garage for the two cars, we planned a 6 x 3 m storage room behind the garage. The total garage is thus 6 x 9 m in size. This storage room behind the garage is not free either, but it costs less than a cellar or partial cellar of the same size as the storage room of the garage. Therefore, that was the cheaper solution. Moreover, as I said, I am not a fan of cellars. I just do not like the feeling and do not feel comfortable in basements. Therefore, I would not build a cellar for myself even if it were not so expensive.

By the way, a cellar does not protect against cluttering the garage. As several have already said here: it is probably just a matter of personality, some tend to clutter, others do not. And those who tend to do so do not stop at the garage, even if a cellar is present.

With a built-up area of 100 m², the basement therefore costs about 60,000 euros (rough estimate).

Of course, it is not free. My point is, creating the same area above ground in the house costs you around 150,000. A garage with 37 sqm of built-up area in solid construction also costs you almost 50,000. It is just confusing when it is said in general that a basement is (too) expensive.

That is a great solution (i.e., garage extension) if there is enough space and the building envelope allows it. Unfortunately, that is not always the case. Especially in times when plots of land are getting smaller and smaller...
We also have a slightly extended garage, but that’s where our bicycles will go, as we have quite a few..., plus a motorcycle, and some garden supplies.

Personally, we would prefer the workshop to be on the ground floor or somehow at ground level, but unfortunately there is not enough space. Something like that could also go into an appropriate garden shed. But that also requires space (which we don’t have).

Therefore, regarding this question, there is probably no "right" or "wrong," but only a decision that is right for the respective situation, and that decision can sometimes go one way and sometimes the other. And the decision will likely also be influenced by individual preferences and habits.

So, to return to the original question: whether a basement still makes sense today or not depends on the respective situation. I can definitely imagine it without a basement, but due to my storage requirements and my available space, I have no other choice.
If you have a large plot of land and the possibilities, much can also be accommodated on the ground floor. With regard to barrier-free living in old age, that is certainly not a bad thing. But it is not always feasible or sensible.

Therefore, there is probably no "right" or "wrong" in the question, but only a decision that is right in the respective situation, and that decision can be one way or the other. And the decision will probably also be shaped by the respective preferences and habits.

I completely agree with you. The decision for or against a basement largely depends on the circumstances. Size of the plot, preferences of the builders, certain rooms the house should have (party room, etc.). Especially the size of the plot is an issue, and I know that in urban areas there is often no possibility to build larger above ground. Therefore, a basement is a good alternative to create space, if desired. Since we are building very rurally, the land prices here are still low and the plots accordingly not too small – although our plot is far from huge with 632 m², it is large enough to build a house with 105 m² floor area + double garage on it.

We are also quite rural (800 inhabitants, of which 400 have horns *g*), but since we are building onto my parents' property, space is limited...