For what it’s worth, if the file name ends with DLL it’s VST 2.x. If it ends in .vst3 it’s a VST3. Also, VST3s aren’t installed in your VSTPlugins folders. At least on Windows, VST3 files usually go under C:\Program Files\Common Files\VST3 or in a VST3 folder inside your Cubase install directory (only for plugins bundled with Cubase).