Not sure what exactly you are looking for here but it seems like system dependencies are discouraged by Maven: https://maven.apache.org/guides/introduction/introduction-to-dependency-mechanism.html#system-dependencies

What would this feature help you achieve? Could there be another way of achieving that without relying on deprecated features?

Because in some cases, the jar files used are provided by third-party companies and not published in any Maven repository; So at this point, it needs to be used as a system scope and packaged into a jar package during exec maven package; Spring boot maven plugin supports configuration <includeSystemScope>true</includeSystemScope> which can effectively solve my problem; But Hilla will report an error.
For now. I install the jar file with mvn install:install-file to solve this problem. But it is not a good experience

The correct place to address this would probably be in https://github.com/vaadin/flow/blob/e973f16fe406fde24b0a6d987c5b9a9d9a2d5784/flow-plugins/flow-maven-plugin/src/main/java/com/vaadin/flow/plugin/maven/FlowModeAbstractMojo.java#L245-L248

For reference, this is the discussion that lead to including this feature in Spring Boot. spring-projects/spring-boot#2224

To me, the key point is really this comment:

Usecase where I see this is with some wrapper libraries not available in maven - and CI server being operated centrally and not liking people adding stuff to repositories on their own, or running own repositories.

...and here's a discussion related to why the Maven maintainers think that the system scope should be deprecated: https://issues.apache.org/jira/browse/MNG-6523

My interpretation is that Maven has this feature for other purposes and the Maven maintainers think the way it's actually used is wrong and shouldn't be needed in a perfect world. They think you should make the world perfect rather than relying on Maven to officially support the current state of the world.

Let's follow what Spring Boot does here: add a property flag that enables this.

As part of the solution, let us verify that Hilla supports entities from system dependencies.