I was recently trying to install OptiFine for Minecraft on Fedora 40 with KDE Plasma on Wayland. I ran the OptiFine JAR file in Konsole, and received the error below:

java.awt.HeadlessException: 
No X11 DISPLAY variable was set,
or no headful library support was found,
but this program performed an operation which requires it,

        at java.desktop/java.awt.GraphicsEnvironment.checkHeadless(GraphicsEnvironment.java:166)
        at java.desktop/java.awt.Window.<init>(Window.java:553)
        at java.desktop/java.awt.Frame.<init>(Frame.java:428)
        at java.desktop/java.awt.Frame.<init>(Frame.java:393)
        at java.desktop/javax.swing.JFrame.<init>(JFrame.java:180)
        at optifine.InstallerFrame.<init>(InstallerFrame.java:55)
        at optifine.InstallerFrame.main(InstallerFrame.java:115)
Exception in thread "main" java.awt.HeadlessException: 
No X11 DISPLAY variable was set,
or no headful library support was found,
but this program performed an operation which requires it,

        at java.desktop/java.awt.GraphicsEnvironment.checkHeadless(GraphicsEnvironment.java:166)
        at java.desktop/java.awt.Window.<init>(Window.java:553)
        at java.desktop/java.awt.Frame.<init>(Frame.java:428)
        at java.desktop/java.awt.Frame.<init>(Frame.java:393)
        at java.desktop/javax.swing.SwingUtilities$SharedOwnerFrame.<init>(SwingUtilities.java:1925)
        at java.desktop/javax.swing.SwingUtilities.getSharedOwnerFrame(SwingUtilities.java:2001)
        at java.desktop/javax.swing.JOptionPane.getRootFrame(JOptionPane.java:1696)
        at java.desktop/javax.swing.JOptionPane.showOptionDialog(JOptionPane.java:875)
        at java.desktop/javax.swing.JOptionPane.showMessageDialog(JOptionPane.java:677)
        at java.desktop/javax.swing.JOptionPane.showMessageDialog(JOptionPane.java:648)
        at optifine.InstallerFrame.main(InstallerFrame.java:138)

I read from other forum posts that to specify the X11 display variable, I needed to run export DISPLAY=0. I did this, but it didn’t change anything. I also tired starting an X-server, but that didn’t do anything either. Additionally, I tried running the JAR in GNOME on Xorg, but to no avail either.