Construction costs are currently skyrocketing

The ECB's interest rate hikes will NOT (!) be responsible for a further increase in mortgage rates.

They also have nothing to do with each other at first because we are at significantly different points on the yield curve. Central banks control the very short end through the key interest rate. This affects the long end in the sense that long-term investors want a risk premium for committing themselves long-term. Otherwise, the correlation between the key interest rate and the 10-year or even much longer maturities is rather loose.

Much more impactful here is that the ECB is stopping its bond purchases and the FED is already planning to gradually sell its bonds. So far, risk premiums in Europe were practically not enforceable; the ECB bought almost everything at almost any price. An institutional investor who, due to regulations, must invest in government bonds with corresponding credit quality had to play along. Now that is changing. The ECB is dropping out as a buyer, and across the pond there are likely to be some bargains as the FED starts selling. Even the tapering of bond purchases has led to rising yields and indirectly increased mortgage rates.

Is it already noticeable that the massive decline in steel is being passed on?

At the moment, I don’t have the impression that it is being passed on. With wood, it apparently already looks better again. But with a new construction project nearby (terraced houses, new construction through a developer), it is explicitly stated in the online tender that there will be construction cost increases approximately every six weeks and that the fixed price cannot be guaranteed, or you have to be quick to conclude the contract (the wording in the advertisement is somewhat confusing).

Update on window costs/roller shutters/etc.:

5 offers from companies in the surrounding area (NRW). Refer to double-glazed, plastic windows, plastic roller shutters on each window, 17 windows, 1 lift-and-slide door, standard front door (without filling). However, the windows are very large (partly floor-to-ceiling and panoramic):

Provider 1: €30,000, Provider 2: €38,000, Providers 3, 4 and 5: approx. €45,000

Provider 1 manufactures themselves and therefore has significantly fewer problems. After adjustments to triple glazing, partial venetian blinds, front door with filling, security fittings and lockable window handles: €40,000. A good offer in the current times (including installation, foam, measuring, etc.)

Foam is possibly already a bad sign. Today, [Kompriband] is actually used. Installation quality is more important than element quality. From a certain level, manufacturers no longer differ significantly. Possibly only in appearance.

Foam might already be a bad sign. Nowadays, compressible tape is actually used. Installation quality is more important than component quality. From a certain level on, manufacturers don’t differ significantly anymore. Maybe only in the appearance.

To be honest, the term was included because I don’t know exactly how the company installs it. I also don’t know the different methods and am therefore grateful for this hint. I will clarify this again beforehand.

Foam is perhaps already a bad sign. Nowadays, compriband is usually used. Installation quality is more important than element quality. Beyond a certain level, manufacturers no longer differ significantly. Maybe only in appearance.

Of course, compriband and sealing tape are used. Foam is not airtight anyway.
However, this has been an absolute standard for at least 10 years.
It is important that all elements are properly dowelled and that no money is saved on the material there.
I can't say anything about the price, it is too individual which manufacturer for the profile?
We have Schüco and Ug 0.5 W/m2 6-chamber profile.
Otherwise, yes! Proper installation is the most important factor!
For example, we have oversize, our windows are 255 cm high, front door as well, that cost more, but it wasn’t excessive.
Aluminum front door 2 m wide, lift-and-slide door (3.2x2.55), 24 windows, 50% floor-to-ceiling, 6 m sectional door all anthracite inside + outside including raffstores and blackout blinds cost 34k in 2021.

Price comparison is, as said, difficult, but prices have risen about 25% in 12 months.