Thanks to Gerddieter and 11ant for the additional opinions. Precisely because the recommended approaches go in different directions, the contributions are very helpful for our formation of opinion. Overall, we can see a bit more clearly now.
We have set a deadline for the schedule with the architect. If something comes up, we will demand a weekly update of the plan and insight into the construction log.
Additionally, consult a lawyer to find out whether, when the final invoice for HOAI Phase 8 arrives, proof should be requested that the schedule and log have been maintained throughout the entire phase and, if necessary, reduce the payment.
We already thought we were extremely forward-looking a year ago when we decided not to organize the renovation ourselves but to hire an architect who "takes care of everything" :(
Further opinions are very welcome.