What should I do if the renovation of the new house is completed and I have checked in, but I can be told by the property that the flue exhaust needs to be replaced?

You can report to the property company and the industry Committee and urge the owners to stop the corresponding behavior and restore to the original state. The flue belongs to the public area owned by the owner, and the owner shall not occupy it privately. If there is a corresponding situation, you can report it to the property management company and the industry Committee and ask the owners to stop the corresponding behavior and restore the original state. If the owner refuses to rectify, he can complain to the competent department of the Ministry of Housing and Urban-Rural Development, and the competent department will carry out administrative law enforcement and forcibly restore the original state. If the owner's behavior causes damage to the property or rights of other owners, the relevant owners may bring a lawsuit to the people's court, requiring the owners to bear the responsibilities of stopping the infringement, restoring the original state and compensating for the losses.