Just add double quotes on the full path, the specific reason is unknown.
**
protoc --cpp_out=/ test.protoc
protoc --grpc_out=./ plugin=protoc-gen-grpc=“D:\Desktop\grpc\grpc\Build_GRPC\Debug\grpc_cpp_plugin.exe” test.protoc
**
The full path above is the full path of your exe, it may be different from mine