No completion and warranty bond - retention?

Hello, our house construction is progressing well, the screed will be installed at the end of the week. So far, we have adhered to the payment schedule (except for minor withholdings due to defects). Unfortunately, it has only now really become clear to me that we have already paid the majority of the total costs, but the payment schedule does not really correspond to the services rendered. Now to my question: Our construction contract with the developer does not contain a clause on completion or warranty guarantees. So we probably have not agreed anything in this regard and the Construction Code applies. What does that look like? Is it still possible to make a flat-rate withholding for completion and warranty now? Best regards Simon