Is it sensible to build a new semi-detached house without the KfW standard?

Plots of land have tended to be the biggest obstacle in house construction ever since 100% financing at 1.x% was pushed on people. So if you are very likely to get a plot of land, then go ahead and play the lottery.

Recently, 3 km away, there was a semi-detached house KfW55, 162m², including paving work, garage with electric gate, developed attic with underfloor heating for €380,000.

What is "recently"? Calculate 5% p.a. on construction prices; if this was two years ago, the current price would be (380k € - 60k € land) = 320k € * 10% = 352k € construction costs plus 60k € land = 412k € total costs. Painting and flooring almost always cost extra.

Are KfW 100 / Energy Saving Ordinance 2016 houses still state of the art today or should one only buy KfW70 or better?

What until four years ago was still considered KfW-70 is today the minimum standard according to the Energy Saving Ordinance, meaning "KfW-100" (= Energy Saving Ordinance from before 2016, the term KfW-100 actually does not really exist) is only found in existing buildings. If someone offers a new build today, it can only comply with the Energy Saving Ordinance 2016 = KfW-70.

Even if the market may bear the price, my decision in case of doubt would be not to buy and continue renting. Better than getting stuck with an overpriced property.

Understandable, since you also don’t like the features of the property. If it’s purely about the price, think again about the 5% construction price increases: That is additional costs of €15k p.a. on a €300k construction sum... You first have to have that! €1,200 savings rate, month after month... and that just to stay in the same place.

Are you so tied to your location? Maybe there's something 50km further away? Around here, there is usually a new construction area somewhere within a 50km radius every year.

just as an idea, we bought the building land in 2018 for €180 per m², in 2019 the plot right next to us, same size, was sold for 300m². not offered. sold. your land prices from last year are worthless today. if it has a gas heating system it doesn’t matter. it costs nothing. beautiful is different, you just have to know how urgently you are looking for a house and how much money you have.

Even if the market may allow the price, my decision in case of doubt would be not to buy and to continue renting. Better than tying yourself to an overpriced property

Why not buy an apartment then and see how it goes? At least you’re not throwing rent money out the window.

well, because with assumed 10% acquisition ancillary costs plus moving and an assumed 4% rental yield, you have to live in the apartment for almost 3 years before reaching the breakeven. then renting is already better and I assume that the OP is already doing exactly this.

Have you all not heard the shot? Because of a few kWh/m2*a on paper, an otherwise seemingly suitable house should not be bought? It simply doesn't matter. The insulation craze has really taken hold in people's minds. And the lathing in the attic is also still decisive? You can do that in a weekend. If the location and layout fit as you say, go for it...