When driving 2021 Buick Envision, the windshield and side windows do not defrost with HVAC set to defrost mode. Service Climate system is displayed on dash. Vehicle was inspected by dealer finding replacement of HVAC case half housing required on 1/22/24 ( a year ago). GM (M) has been in contact but has failed to provide a solution after 1 year of trying to obtain a part from their system. This condition results in immediate fogging condition of all windows without warning presenting a visibility safety hazard for the driver and surrounding vehicles. Sorry GM, but a rag to wipe the window is not a good solution. It has been a year with no urgency from GM to remedy the issue. This is deemed a critical function for safety and GM ds not take it seriously.