People sell all kinds of things that are based on things in the public domain, because people are paying for someone else to go through the steps of creating it. Creating new works based on something in the public domain, like a 3D model of a mouse that is in the public domain, is a new work that can be copyrighted.
This person could sell the 3D files they created because creating the 3D files is a new creation. Someone else could also create the exact same 3D file from scratch and this person could not claim copyright because the subject of the 3D file is in the public domain.
Anyone can copy the Disney film version outright because the film is in the public domain.
People sell all kinds of things that are based on things in the public domain, because people are paying for someone else to go through the steps of creating it. Creating new works based on something in the public domain, like a 3D model of a mouse that is in the public domain, is a new work that can be copyrighted.
This person could sell the 3D files they created because creating the 3D files is a new creation. Someone else could also create the exact same 3D file from scratch and this person could not claim copyright because the subject of the 3D file is in the public domain.
Anyone can copy the Disney film version outright because the film is in the public domain.