Talk to the bank. Mine wanted to have proof at closing through photos of what was renovated/refurbished and invoices for the conversion measures roughly corresponding to the amount I borrowed beyond the purchase price. However, since we used several tens of thousands of euros completely differently than originally planned, the bank also received completely different invoices.
This only really matters if you draw down the loans completely. If you fall short of the loan amount because you don’t renovate the bathroom, then it is probably not the slightly lower lending value that is the problem, but rather the fact that the bank has to repay the undrawn amount, for example to KfW or the state/federal bank.
It may be that this then costs a "penalty interest."
But you can avoid this by, for example, keeping €15,000 in equity for the renovation of the bathroom. If everything else works out, you do the bathroom renovation with your own funds, which the bank doesn’t care about. If the equity is needed for other things, then the bathroom renovation simply doesn’t happen, which the bank also doesn’t care about because it doesn’t even appear on the list of renovations/upgrades.
Best regards
Dirk Grafe