VRoid Studio might fail to start due to the presence of antivirus software on your computer.
Try removing VRoid Studio from the monitoring target of your antivirus.
If the issue isn't solved, please refer to the following articles.
Also, please make sure you're using the latest version of VRoid Studio.
You can download the latest version here.
Also, if you are using VRoid Studio 0.8.2 or earlier, there was a bug in which, in the event of a Windows Security block, files such as models and settings were incorrectly saved in AAA\vroid (AAA stands for the name of the directory where you installed VRoid Studio).
Please copy the contents of the directory to the correct location "C:\Users\(Your username, OneDrive, etc.)\Documents\vroid".