Running the executable file (.sh) from terminal gives this output
[akash@fedora Downloads]$ ./JDownloader2Setup_unix_nojre.sh
Starting Installer ...
java.lang.NoClassDefFoundError: Could not initialize class java.awt.Toolkit
at java.desktop/java.awt.Color.<clinit>(Color.java:277)
at com.install4j.runtime.installer.frontend.GUIHelper.<clinit>(GUIHelper.java:46)
at com.install4j.runtime.installer.helper.InstallerUtil.reportException(InstallerUtil.java:1327)
at com.install4j.runtime.installer.Installer.main(Installer.java:48)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:568)
at com.exe4j.runtime.LauncherEngine.launch(LauncherEngine.java:84)
at com.install4j.runtime.launcher.UnixLauncher.start(UnixLauncher.java:69)
at install4j.Installer378667612.main(Unknown Source)
I don't know if there is any other output I have to send since I am still pretty new to Linux.
If anyone else got same error. Just remove your JRE/JDK and install it again.
Note- It might remove some other apps like libreoffice and stuff, so save files and make backups.