The general recommendation of many predecessors to consult a specialist lawyer for construction law is the only sensible approach.
After the contractual partner (developer) has not fulfilled their contractual obligations to a significant extent, the other party usually has the right to extraordinary termination. This would relieve the bank's obligation to secure the purchase price, so the capital would have to be repaid.
Alternatively, you can have the defects established in court as part of a preservation of evidence procedure. However, I doubt that you would want to have the developer work for you again.
Both can only be determined and litigated by a suitable lawyer.
In addition, lawyers have the legal and rhetorical skills to build an extensive threat scenario. The developer will only react when under pressure.
Even though this approach is the only way to protect your interests, there is always a litigation risk in such disputes. You could end up bearing all the costs in the event of an adverse outcome.
Only a lawyer can also review this point.