You cannot download a model that was uploaded to VRoid Hub, then open it in VRoid Studio.
Even if you made the model yourself in VRoid Studio, then uploaded it to VRoid Hub, you cannot re-download it and open it in VRoid Studio.
The file format for uploading and downloading models on VRoid Hub is the ".vrm" format.
The file format in which you can edit models in VRoid Studio is the ".vroid" format.
Therefore, we apologize for the inconvenience, but we ask that you upload only models in .vroid format to VRoid Studio.