thanks at the user from stackoverflow
https://stackoverflow.com/questions/73456501/plantuml-activity-diagram-special-box-layout-output-is-needed
Activity Diagrams in UML have certain rules. Using split is probably a bad idea, as it's intended for the SDL aspect of PlantUML.
Perhaps you can try with fork if you want to show the output in a separate swimlane:
@startuml Test1
title Flowchart
|System 1|
start
:Step1;
:Step2;
:Step3;
fork
:Step 4;
|System 2|
fork again
:Output of Step3]
stop
|System 1|
end fork
stop
@enduml
I put a stop at the end of the output (which is now an object using the ] ending) to prevent the line rejoining the flow in System 1.
Another alternative is to use the legacy syntax for Activity diagrams, which doesn't allow for swimlanes, but can do partitions.
@startuml Test2
title Flowchart
partition "System 1" {
(*) --> "Step 1"
--> "Step 2"
--> "Step 3"
--> "Step 4"
--> (*)
}
partition "System 2" {
"Step 3" -> "<< object >>\nOutput of Step 3"
}
@enduml
In the legacy syntax for Activity Diagrams, it's not possible (as far as I know) to make an "object" (rectangle) shape.