Additional costs of a finished house

The property tax also depends significantly on the local multiplier [Hebesatz B]. For us, that alone amounts to almost a four-figure sum...

Photovoltaics on the roof with approx. 9.8 kWp (annual yield estimated by PVGIS 8170 kWh),

Have you already included the yield in the following item? And is heating perhaps already included? Or where is "the heating"?

Electricity €910.00

Roughly (or banks often assume €2.5–3 per sqm including reserves for repairs of 50 cents at the beginning).

So some things are missing from your plausibility check, or not obvious, or are "quite cheap."

In general, some things are very location-dependent and vary greatly in Germany, such as water/sewage, property tax due to the multiplier rate.

For the following item, I would guess that no waiver of underinsurance (min €650 per sqm), no natural hazard coverage, and no glass breakage are included:

Household insurance. €110.00

...and never forget the GEZ besides heating and maintenance costs

Regards

We consume quite a lot of water (approx. 120m³ per year) and it comes to around 400.- per month. However, also 24 degrees in the living room etc. But 20.- one way or 25.- the other doesn’t really make a difference with an investment of 400 k€, does it?

Who has frostbite at your place? 24 degrees in the living room? I already get hot flashes at 22 degrees...

I find it cozy when you don't have to shiver in short sleep shorts in front of the TV at night, the woman finds it "appropriate" anyway, like most. And as I said, for most people the house will swallow between 1500 and 2000 a month (in our area with costs of about 400,000 € for an average house). 20 here or there doesn't really matter then, I'd rather be cozier than save 1000 kWh per year on heating. That's why the extra cost for KfW xyz often isn't worth it either, you hardly make that back on heating costs...