Construction costs are currently skyrocketing

It is simply the case that the funds are no longer there because of Corona.

Is that allowed? Hopefully, there are contrary court rulings on this.

Of course, it is allowed to review each person's job with regard to the job description.
If you only perform half of the tasks or, for example, do not do 50% autonomous work but are paid accordingly, then the job can be downgraded. What applies to the "right to existence" is to be reviewed as well, also by trade unions etc.

I just wanted to mention it, in parallel, when wage increases and the like are being talked about here.
From the perspective of the overall economy, this is not the case.

How it will be for us, I don’t know yet. So far, I have understood that the tiles, sanitary fixtures, sockets/socket locations, etc. are determined during the sampling phase.

If all of that is supposed to go through your general contractor or will, then it can get expensive, yes. Socket at that time via the GC €50, via the electrician €26.50. And so on.

Topics we will deal with: type/quality/colors/design of the facades and the interior walls/ceilings. For example, we would like white ceilings but not white walls. Type of doors: glass or non-glass, how many panels. Color/security class of the windows. Mullion distribution in the windows, depending on that the size of the windows, terrace doors or French doors everywhere on the ground floor (that seems to make a difference for "entry-exit"), and much more.

Painting work was an extra service for us, which was done by a painter of our own choice (outsourced). The GC had nothing to do with that. If I were you, I would have already inquired about the price of one thing or another in advance and included it as an item in the contract. But that is discussed here in the forum in the relevant subforums about how to do it.

Individual salary/wage determinations were/are currently difficult. Therefore, exceptionally on a flat-rate basis.

we signed a one-year price lock contract in December 2020.
When asked, we were told that we don’t have to worry at all, they still have good conditions and wood stored.
We are building a solid wood house with a smaller (but not regional) supplier.
The price remains the same for us. However, the builder only does the shell, meaning we continue with self-performance and individual contracting.

We were already told by heating/plumbing that prices will increase somewhat in November, but how much, he won’t know until then.

The electrician told us in May that if we start at the end of the year, it will be €1,500 more expensive (on a total of €14,000). However, the first offer was also from December 2020.

We only selected samples with the house manufacturer for the front door and the windows. There it only got more expensive because we chose a different wood for the windows (+€1,450 for spruce instead of pine) and a different handle set (€253) and RAL paint for the front door (€230).

So we were very worried in between as well, but it seems to be calming down slowly and so far it is absolutely bearable for us. And we also don’t have big buffers.

If all of this is supposed to go through your general contractor or will go through them, then it can get expensive, yes.
Socket back then via GC €50, via the electrician €26.50. Etc.

We still hope not to need too many additional sockets. In theory, we can take out the electrical work, but we don’t want to. We want a nearly "turnkey" house. Given the current situation with tradespeople, we probably wouldn’t find anyone.

The painting work with us was an EL who contracted a painter of his own choice (external assignment). The GC had nothing to do with that.

Here, too: in theory, we can take out the painting work, but we don’t want to. We want a nearly "turnkey" house. Given the current situation with tradespeople, we probably wouldn’t find anyone.

If I were in your place, I would have already asked for prices in advance for one thing or another and included them as line items in the contract. But it says here on the forum in the corresponding subforums how to do that.

We were pressed for time because we wanted to order before the upcoming price increase. We don’t know if that was a sales trick. We know the prices for, for example, painting work, but only for the standard, not for deviations from the standard. During the selection phase, depending on the price difference, we will also decide whether to take "Raufaser" *buuuuuhhhhhh*, a nice type of plaster, or even fine wallpapers. :)

We still hope not to need too many additional sockets.

The sentence irritates me. You will have a construction service description that shows (in pieces) what you get. So it is roughly clear what is still needed, such as sockets, lighting outlets, switches, network sockets (which are usually never included), ...