Download JD-GUI to open JAR file and explore Java source code file (.class .java)
Click menu "File → Open File..." or just drag-and-drop the JAR file in the JD-GUI window scala3-compiler_3-3.2.2-RC1-bin-20221101-d84007c-NIGHTLY+1-extensible-repl.jar file.
Once you open a JAR file, all the java classes in the JAR file will be displayed.