Interior construction KS/brick/metal stud frame

Contractually, sand-lime brick or brick was agreed upon. They just want a signature stating that the contract is being deviated from and ws111 may be used. Alternatively, we could stick with brick. Therefore, my question is what is better; if so, I would want to take at least ws112 with f90. The gypsum boards, however, also sound really good.

The walls to the outside are either house walls or load-bearing sand-lime brick 24mm walls to other apartments/hallways. Therefore, the noise would only be within the apartment, but I simply have the feeling that sand-lime brick or brick is the higher-quality option compared to ws111.

If drywall, then I would only choose a w112. For fire protection anyway, but also for the rest. The wall itself simply has more mass, which is better for insulation. If you want to attach something to it, the double-boarded version also has an advantage. However, with drywall, always keep in mind that especially heavy items should preferably be anchored in the studs with metal hollow wall anchors.

Okay, and how does brick compare? Bricks with a density of 0.8kg/dm^3 are to be used.

Sorry,
I may possibly misunderstand the initial situation.
You have a contract for item X for amount Y with quality and execution Z.
Afterwards, someone wants to give you something clearly different for the same? price?

Wouldn't it be the responsibility of the builders to prepare the new building so that the statics
fit and the stones described in the construction service description can be used.
In other words: They should simply fulfill their contract.

Yes, exactly that describes the situation. The problem is only that according to the contract, bricks or sand-lime bricks are allowed to be used. For some reason (structural analysis was mentioned) they no longer want to use sand-lime bricks. Which does not necessarily make sense to me as a layperson. Is sand-lime brick that much heavier?

So bricks would have to be used, alternatively they offer us ws111. Although in this case I am totally unsure what to choose.

In the first step I will personally ask for the reason at the beginning of the week and demand insight into the structural analysis. If everything is that clear, my desired solution would be to agree to build important walls for me in sand-lime brick (e.g. kitchen and bathroom) and some others, for example, in drywall.

Alternatively, I would definitely demand ws112 with f90.

My current question is, if the structural analysis all checks out, whether bricks or metal stud frame (initially ws111, I will push for ws112) is better, if that can be said in such general terms. In the email only the advantages of ws111 over bricks were mentioned and among other things it was stated that large pieces break out of the bricks when mounting fasteners. For this reason, it seems as if they wanted to push us to ws111, which in my opinion would be the time/quality/cost favorable solution.

Yes, that exactly describes the situation. The only problem is that according to the contract, bricks or sand-lime bricks are allowed to be used. For some reason (structural analysis was mentioned), they no longer want to use sand-lime bricks.

Who is stopping the construction company from adapting the structural analysis to the bricks? Don't let yourself be taken advantage of...