New construction 2DHH KFW 40 each 150m2 living area as an investment property

What is the market value of the land and house after completion?

What kind of questionnaire is that - it doesn’t seem familiar to me (?)

Net rental yield approx. 5.2% [...] What do you think?

That the troll here is not the OP, but his financial advisor.

how do you get over 5% return here. 21000.-- rent on 650000.-- construction costs less than 3% and that is currently the return on new builds. In some cities even less

No. Even much better. Based on the 30 TE equity to be invested and about 90 TE of already paid-off land, 21 TE rent is actually closer to around 20% return, based on the equity.