How to import plugin to Engine no project and make it work after package?

I created a plugin of blueprintFunctionLibrary .
It works well if I put it to project\Plugins. But it needs a c++ project to rebuild dll and add name to PublicDependencyModuleNames in code. It jumps through too many hoops to use it.
If I put it to UnrealEngine\Engine\Plugins and rebulid by souce code, it need to be set only once . The plugin also can work in blueprint project. It’s so good. But something is wrong when I run a standalone game . The plugin not work after packaged and the problem is showed in the image.

Hope somebody can give me some advice,thank you!