ADDITIONAL SYSTEM INFORMATION :
macOS Sonoma 14.7. Java 23.0.1. OpenJFX 23.0.1.

A DESCRIPTION OF THE PROBLEM :
JavaFX apps fail to properly render some characters. This includes single-codepoint characters like `𐀀`, LINEAR B SYLLABLE B008 A, at decimal codepoint 65.536. Despite every font on my Mac supporting this character, JavaFX apps display striped-box while the very same string appears correctly on the Java console.

For screenshots and discussion, see Stack Overflow:
https://stackoverflow.com/q/79127168/642706



STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Build a string like this:

String text =
        new StringBuilder ( )
                .appendCodePoint ( 65_536 ) // 𐀀 = 65536 = LINEAR B SYLLABLE B008 A
                .toString ( );

Dump to console, where the text appears correctly.

System.out.println ( text );

Put that same text in a JavaFX `TextArea` where it appears incorrectly.

There is already an unresolved bug report for characters composed of multiple codepoints such as man-facepalming 🤦‍♂️ = [129318, 8205, 9794, 65039]. But I filed this bug report for the case of a single codepoint simple character.
https://bugs.openjdk.org/browse/JDK-8309565

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I expect to see that single character appear in the JavaFX UI:
𐀀
ACTUAL -
Instead I see a striped box.

---------- BEGIN SOURCE ----------
package work.basil.example.exunicodeglyph;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.TextArea;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

import java.io.IOException;

public class HelloApplication extends Application
{
    @Override
    public void start ( Stage stage ) throws IOException
    {
        Scene scene = this.makeScene ( );
        stage.setTitle ( "Hello!" );
        stage.setScene ( scene );
        stage.show ( );
    }

    private Scene makeScene ( )
    {
        // Widgets
        TextArea textArea = new TextArea ( );
String text =
        new StringBuilder ( )
                .appendCodePoint ( 65_536 ) // 𐀀 = 65536 = LINEAR B SYLLABLE B008 A
                .append ( "\n" )
                .appendCodePoint ( 129_318 ) // 129_318 = 🤦 = FACE PALM
                .append ( "\n" )
                .append ( "🤦‍♂️" ) // man facepalming = 🤦‍♂️ = [129318, 8205, 9794, 65039]
                .append ( "\n" )
                .append ( "« fin »" )
                .toString ( );
        System.out.println ( text );
        textArea.textProperty ( ).set ( text );

        // Arrange
        StackPane root = new StackPane ( );
        root.getChildren ( ).add ( textArea );
        return new Scene ( root , 320 , 240 );
    }

    public static void main ( String[] args )
    {
        HelloApplication.launch ( );
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
None.

FREQUENCY : always