Assessment of the cause of mold after renovation

I would definitely first document all adjoining rooms and, if applicable, exterior views by photo (current condition). If possible, check the water pipe routes to see if anything lies in the corresponding area. Then also uncover the floor, meaning the elements that are damp underneath and, if possible, let them dry or provide new panels immediately. And then I would get in touch with the insurance if there is an appropriate policy. Possibly they can show you the next steps?