How to build according to the Building Energy Act or EH55 or EH40

Just did it.
There I stand now, poor fool,
And am no wiser than before!
Because simply a number is thrown into the room and not concretely justified in any way. And this also contradicts my experience from construction practice, because which part should require more maintenance now? Walls? Windows? Ventilation?
By the process of elimination, only the ventilation remains, but according to the Building Energy Act, you do not necessarily build without it (not even in residential construction, because otherwise you have noise issues due to mold after a few years). And for the saved 8000 kWh = approx. 2500€ per year, I can replace the fans in the apartment building one after another.

Unfortunately, as an absolute layman, I cannot give you an answer to that.
Are subsidized heat pumps perhaps more expensive and possibly more prone to faults?

I have just read a study about the life cycle costs of a 12-unit apartment building.

What you kindly "linked" to us ;-) I would not call a "study," but only a brief summary of a study for the impatient-superficial readers of a trade magazine ;-) What is your intention with it: to share the information or your amazement with us, or do you actually just want to ask us with this study as a hook/introduction whether, in our assessment, you should build your own home according to today's legal standard or the standard of a few years from now? If the latter applies, you can already read my opinion on this here several times, briefly summarized: Legally insured / below the highest tax rate, you do not belong to the privileged circle for whom avant-garde / early adopting subsidized future standards "pay off." You are still allowed to do it, but economically it is then a luxury.

What is your intention here: to share the information or your amazement about it with us, or do you actually want to use this study as a starting point/introduction to ask us whether, in our opinion, you should build your own home according to today's legal standard or that of a few years from now?

You get the price difference between the Building Energy Act and EH40 from the architect or prefab house seller. I can't imagine the latter telling their customers that an EH40 house from them is more expensive not only now but over the entire life cycle. Rather, it is advertised that you spend a bit more now and take advantage of subsidies, then you have lower costs later.

What I wanted to point out is that this is not the case.

What I linked is of course not the study, but without much effort you can download it for free. The source is indicated in the article. The study also deals with single-family houses.

Are subsidized heat pumps perhaps more expensive and possibly more prone to failure?

The building envelope initially has nothing to do with heat generation. The building envelope consists of walls, windows, roof insulation/upper floor ceiling, basement ceilings or floor slab insulation. From EH40 onwards, ventilation with heat recovery is also mandatory, but that does not automatically mean that you wouldn't install it otherwise. Even a bargain hunter like Town & Country installs Lunos fans as standard. For rented apartments, mechanical ventilation is worthwhile anyway, as it reduces mold issues.
Looking at the points, it is clear that there isn't much maintenance effort involved. Whether you stick 10 cm EPS onto a concrete wall or 16 cm in residential construction... if it's done properly, it lasts a long time, and if it's done poorly, you have the effort with both. Upper floor ceiling/roof and basement ceiling hardly play a role in large multi-family houses anyway, since most apartments are located between two other apartments. There is no maintenance effort either. The only remaining difference is the ventilation.
Those interested in the original can download it for free from ARGE Kiel (arge kiel Wohnungsbau - THG emissions, energy consumption, and costs in the life cycle). But I can disappoint everyone right away, because there is no derivation or justification of the higher maintenance and servicing costs there.

It really depends on whether you have the money that EH40 costs more or not. If you have it, you might save money in the long run. If you don't and currently have to finance at 4%, then the amortization outlook looks rather poor. Especially since an ETICS, no matter how good it is and how well it was installed, will eventually reach the end of its lifespan... whether that's 20 years or 50 years. Like a roof or windows. But I've never heard of having to replace masonry after xx years...

It strongly depends on whether you have the money that the EH40 costs more or not.
If you have it, then you might save money in the long run. If you don’t have it and currently have to finance at 4%, then the amortization looks rather bad.

Not at all.
The study aims to say that higher costs arise over the life cycle of the EH40 house and these probably cannot be compensated for by the savings in energy consumption.
This considers maintenance, upkeep, and replacement.

I also find the different maintenance costs between EH55 and EH40 suspicious.