Can not load an unsigned System Extension

Hi every one.


I am a newbie for MacOS driver development. Currently, I am trying to test a simple System Extension base on Driver Kit in MacOS Catalina.
My develop environment: Mac Mini running MacOS Catalina, Xcode 11.4, free developer account.
I download an open source of USB driver in this link: https://github.com/knightsc/USBApp/tree/master/USBApp
This source code is very simple. To build it, I have to setting "Don't code sign" in Xcode because I have only free developer account. The source is built successfully, but when I load it, it show me an error message: "the operation couldn’t be completed. (OSSystemExtensionErrorDomain error 8.)". As I look up, the error 8 is mean invalid signature. But in my Mac mini, I already disabled SIP and run the command "systemextensionsctl developer on". I can load an unsigned Kernel extension normally.
So I don't know why I can not load an unsigned System Extension in my machine?

Please help me, thank you for reading.