freeplane always crashes when running with openjdk-25-jre or openjdk-26-jre,
running with:

env JAVA_HOME=/usr/lib/jvm/java-25-openjdk-amd64 freeplane
env JAVA_HOME=/usr/lib/jvm/java-26-openjdk-amd64 freeplane

The exception is:

java.lang.UnsupportedOperationException: Setting a system-wide Policy object is
not supported
        at java.base/java.security.Policy.setPolicy(Policy.java:114)
        at
org.freeplane.plugin.script.ScriptingPolicy.installRestrictingPolicy(ScriptingPolicy.java:112)
        at
org.freeplane.plugin.script.ScriptingRegistration.register(ScriptingRegistration.java:184)
        at
org.freeplane.plugin.script.ScriptingRegistration.<init>(ScriptingRegistration.java:142)
        at
org.freeplane.plugin.script.Activator$1.installExtension(Activator.java:26)
        at
org.freeplane.main.osgi.ActivatorImpl$OsgiExtentionInstaller.installExtensions(ActivatorImpl.java:280)
        at
org.freeplane.main.osgi.ActivatorImpl.installControllerExtensions(ActivatorImpl.java:296)
        at
org.freeplane.main.osgi.ActivatorImpl.startFramework(ActivatorImpl.java:215)
        at org.freeplane.main.osgi.ActivatorImpl.start(ActivatorImpl.java:109)
        at org.freeplane.main.osgi.Activator.start(Activator.java:35)
        at org.knopflerfish.framework.BundleImpl.start0(BundleImpl.java:386)
        at org.knopflerfish.framework.BundleThread.run(BundleThread.java:145)


Newer upstream version 1.13.x won't fix this. It looks like that Freeplane uses
the obsolete Java security manager, so even the latest freeplane doesn't run
with Java 24 or later.
(https://github.com/freeplane/freeplane/discussions/2124)