It seems there is no connection to the KryoFlux board when running the GUI without 'sudo'. Unfortunately, 'sudo' is not available here on Debian by default:
su -
java -jar kryoflux-ui.jar
Exception in thread "AWT-EventQueue-0" java.awt.HeadlessException:
No X11 DISPLAY variable was set, but this program performed an operation which requires it.
If DTC runs without root rights the GUI should do it also. If not it will be a matter of java and other java apps will show the same behaivior.
Maybe you installed both "default-jre-headles" and "default-jre". Uninstalling "default-jre-headles" and reinstalling "default-jre" should do the trick without sudoing.
The KryoFlux GUI fails for a number of reasons with any JDK or JRE 10 or later.
The first error is caused by the renaming of the look-and-feel classes: the KryoFlux GUI is looking for “com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel” but JDK 10 and later provide “javax.swing.plaf.nimbus.NimbusLookAndFeel”.
Fixing that (by providing the class under the old name) yields another error: CStreamDecoder checks the Java version, and doesn’t accept “11” as a valid version.
I haven’t looked into this any further, it’s really up to KryoFlux to fix this so that the UI can continue working on current Java releases.