Due to requests of several people and due to the fact that we have A40 4D lion's city, A23 was replaced with 3D version. Thanks to this there is a repaint update released to include the 3D version of A23 also.
You can download the repaint update here: https://gogroupvirtual.eu/omsi/buses#1836
New MAN Lion's City will have the same logic. 18C will be 3-door and 19C will be 4-door.