Contractual penalty in the Building Code contract - new construction

Contracts can be negotiated. You don't have to accept the 50€ with a signature. However, one should not think that one could make a profit from it.

No, why?

Because the general contractor only installed his cheap junk.

Because the general contractor only installed his cheap junk.

You have to explain that. You received a construction service description beforehand, in which the "cheap junk" was actually defined.

Building with a general contractor per se is not wrong. We at the bank are happy about every customer who builds with a general contractor (cost certainty, trade coordination, etc.).

Here someone is venting frustration because apparently something is stuck somewhere, things are not progressing, and rent or availability interest is running longer than planned. Probably no sufficient reserve was calculated. I can understand, it was no different for us (5 months construction stop due to groundwater). But that should not distract from one’s own mistakes... If you want 0.2% per day delay, you should have had that included in the contract. If you want better windows, you should have ordered better windows. By the way, for penalties of this magnitude, you are not "powerful" enough. Maybe a VW or a BASF can get that into their contracts with construction contractors, but certainly not Willi Wutz, one of many building owners who are currently building with your main contractor...

Someone is venting frustration here,

I am correcting myself. Building with my general contractor is rubbish.

That I am frustrated is true, but it is definitely not because of the money. More because of the poor price-performance ratio of my house.

Unfortunately, I trusted the general contractor too much. For a first house, it is okay. I just fear that I won’t be able to build again. The loan installment is simply too high. But I still have a lot of equity that is not committed.

Honestly, the poor value for money of my house.

We can't say anything about your terms/contract/construction performance specification/price because we don't know them.
But usually it is the case that someone takes the cheapest provider and then wonders why they don't get high quality installed.
And what does that have to do with the question now?

And what does this have to do with the question now?

That has nothing to do with the question. We are drifting off here a bit.