Purchase or construction in Berlin / surrounding areas, realistic?

An expert in the industry earns in Berlin usually from 80 K EUR upwards (not only at corporations).

Many "normal" engineers still dream of that after many years.
And again, with 3 years you're no longer a greenhorn, but still far from an expert.

Most start small. And if it’s that easy to rake in the money "up there," both can work their way up within the next 5 years and then basically “shoulder” their own home “with ease.”

I never said that the TE and her partner are experts. I presented what an expert in the industry in Berlin earns. I would associate expertise with about 10 years of relevant professional experience, although that does not mean that everyone with 10 years of professional experience is an expert, nor that all experts must have at least 10 years of experience. But roughly on average across the board. I hardly believe that by that definition an engineering expert anywhere in Germany working full-time earns less than 80 TEUR gross including everything.

But the TE and her partner are no longer career starters, and therefore they should not be satisfied with a salary below entry level. There are quite a few shades of gray between beginner and expert, right?

why? OP asked about the situation. Unfortunately, the income is the dealbreaker for the wishes

Respect, it is enough to point out that the income seems too tight.

Straight from the heart: We wish to arrive. To be for ourselves, to do our thing. Space to be outside, for crafting hobbies, for plants and gardening. Free space. Sociability when we want it, but no constant consideration for neighbors. Just to be undisturbed somehow. If I want to play music at 5 a.m., or my boyfriend wants to tinker until late at night, we don’t want to disturb any neighbors.

As a Berliner who has been following the market in this region for several years among others, the above quote is simply the crux. For your desired or "possibility sum," there is no property on the market in the region East/Northeast of Berlin/surrounding area that will meet these requirements.
From my point of view, the following options remain:

A) move out to the hinterland
B) ownership in the ETW/RH sector
C) keep the rental apartment and purchase a weekend plot (building land), use it as you please, and possibly build later

Regarding A) this was not an option for us until now; we both commute by bike, especially during Corona times it was/is worth gold not to have to use public transport. Rising mobility costs add to this calculation.

Regarding B) we did that. In 2013, we bought a terraced house in a good Berlin location, but at that time with the wish for a later upgrade. This idea has already been mentioned here several times, but I consider it nonsense given the current situation in the region. The additional purchase costs alone on properties over 500k do not make a short-term purchase-project any more economical than going straight for the top. We are now stuck, probably until the kids move out, and will probably proceed with A) afterwards. Of course, this is a luxury problem due to the increase in value, but the initial situation has rather worsened than improved.

Regarding C) don’t you feel any pressure in the apartment? Then do it that way. I have two cases like this in my immediate surroundings, and I somewhat regret not having solved it that way ourselves. In 2013, we also looked at building plots with usable weekend houses, for example in Panketal. The price at the time was 70k, which combined with a nice rental apartment at that time in Pankow for 4 rooms also available for 1200,- warm, would have been the perfect deal from today's perspective.
Especially if no children are planned and income is more about experience than result, this seems an option for you to enjoy beautiful spring, summer, and autumn outdoors with family & friends and at the same time keep commuting and costs at a normal level without later being completely deprived of the building option due to excessive hesitation.

Hello everyone, and thanks for the tips, Knappe Kiste.

There isn’t much new to report at the moment, I was quite busy dealing with other private matters.
In the meantime, we looked at a house that would have fit our budget, but unfortunately it wasn’t for us. Too bad, but too many (expensive) changes would have been necessary for it to be suitable for us.
Then we had a consultation appointment with a construction company quite close by. The appointment had been scheduled for a while; otherwise, after the feedback here, I might not have even arranged one.
But it was still quite interesting, even though I am very skeptical. My boyfriend apparently had a very good feeling, but he hadn’t read on the internet before about all the things that can go wrong ;)
The consultant wanted to finish price calculations for one of the offer houses (with and without kfw funding, once with a basement…) and send them to us, I am still waiting for those. He also quickly looked with us for plots of land and roughly calculated how expensive the plot could be... But since we had basically assumed financing advice for existing properties, and I read something about a 15% buffer here in the forum, this can rather be seen as a rough orientation and first approach to alternatives to existing properties.

Work-wise... we’ll see. Annual reviews are due anyway around the turn of the year.

and I read something about a 15% buffer here in the forum

The "buffer question" is very controversial here. There are a number of builders who manage to build houses at surprisingly low prices with a lot of personal initiative, patience, and also own work or self-organized work. They are often not believed here that it all fits like that, maybe it "is not allowed" either if you have paid more yourself. Maybe it helps you to specify the "buffer" a little in order to better assess it for yourselves. Here lie the "cost traps" that can throw a plan overboard:

[*]Completeness of the contract (if not a general contractor, completeness of contracts) – you must understand what is missing in the contract but still needed, because that costs extra money. [*]Earthworks – Sometimes unexpected things lurk in the ground that affect quantities or soil class. Usually, there is an offer with flat rates per cubic meter per soil class. A fixed price offer can create buffer security, although it may not be the cheapest option. [*]Individual equipment – with the general contractor there is a sampling. Everything you want beyond the standard costs extra. If you plan an amount at the beginning that you accept as a surcharge for equipment, you can reliably decide within this budget. Then no buffer is needed – but spending discipline and oversight are necessary. [*]Construction time delays – if there is an unfavorable overlap between moving out of the apartment and moving into the house, costs can arise.

So it is quite possible to build with significantly less than a 15% buffer; that is in the hands of prudent builders.