Floor plan of a house or living area calculation wrong?

The bank does not care at all about the ID at the 2021 house. [...] Yes, tell the bank what's going on and that's it.

I find the concerns of the OP justified, not to admit meekly to the bank only upon inquiry that the loan security is a dozen square meters smaller than expected. And we have already had cases here where financing commitments (which were based on the customers' creditworthiness but not on the moon price of the property) were corrected and the prospective buyers had to back out.

I could swear that instead of "Gebäudeenergiegesetz" before the page refresh it still said "Gebäudeenergiegesetz(ebenen)". Presumably, an AI (artificial impertinence) is at work here.

I have the impression that it said g g f there. Anyway: there is interest in a house. A bank or financing has not yet been mentioned. When requesting financing, real data is used, no matter where from, a few square meters hardly matter at all. One talks about an approximate living area. You don’t go into financing with an exposé, but with the house. If you don’t have current or real drawings, then you change them.

I find the OP's concerns justified, not meekly admitting to the bank only upon inquiry that the loan collateral is a dozen square meters smaller than expected.

Yes, tell the bank what's going on and that's that.

That's why I added my comment. Withholding something is not proper. My point was only that the bank merely wants to know how "green" or "brown" the house is. G + H finance, for example, no longer does this or only does so if there is also an energy renovation.