I downloaded the plantuml-headless-win-amd64-1.2025.1.zip and extracted the files from it in the local bin directory.
I have a small plantuml file (aa.pu):
@startuml
Alice -> Bob : Hello
@enduml
and ran bin\plantuml-headless.exe -help which showed met the normal (java) help information.
When running bin\plantuml-headless.exe -tpng -o aa.png aa.pu I got a big stack trace with at the top:
java.lang.NoClassDefFoundError: java/util/HashMap
at org.graalvm.nativeimage.builder/com.oracle.svm.core.jni.functions.JNIFunctions.FindClass(JNIFunctions.java:359)
at java.desktop@21.0.6/sun.awt.Win32FontManager.populateFontFileNameMap0(Native Method)
So it might be a lack in my knowledge or that the, windows, native image is incomplete.