Cant Install older 1.12.2 Forge Versions because of Java.net.preferIPv4Stack=true...

Good afternoon dear Forge team, I would like to play a self-compiled modpack in version 1.12.2 with my friend on Nitrado. We always had this well-known io.netty bug there. I strongly assume that it is because I had the latest Forge version on my computer (I reinstalled mc -> no Forge version but problem still exists) but the server only Forge Vanilla v.14.23.5.2847 (1.12. 2). That's why I wanted to download this (and other Forge versions of this MC version 1.12.2, which would have worked) and wanted to install them, but then I always get this error (see below). And now I even have the problem that I can't install a Forge version at all, because this error always comes up. I hope you can help me. Thanks very much

java.net.preferIPv4Stack=true
Exception in thread "main" java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at net.minecraftforge.installer.Java6Gate.main(Java6Gate.java:48)
Caused by: java.lang.ExceptionInInitializerError
    at net.minecraftforge.installer.ClientInstall.getSponsorMessage(ClientInstall.java:401)
    at net.minecraftforge.installer.InstallerAction.getSponsorMessage(InstallerAction.java:60)
    at net.minecraftforge.installer.InstallerPanel.updateFilePath(InstallerPanel.java:334)
    at net.minecraftforge.installer.InstallerPanel.<init>(InstallerPanel.java:315)
    at net.minecraftforge.installer.SimpleInstaller.launchGui(SimpleInstaller.java:167)
    at net.minecraftforge.installer.SimpleInstaller.main(SimpleInstaller.java:54)
    ... 5 more
Caused by: java.lang.ArrayIndexOutOfBoundsException: 1
    at net.minecraftforge.installer.MirrorData.buildMirrorList(MirrorData.java:84)
    at net.minecraftforge.installer.MirrorData.<init>(MirrorData.java:63)
    at net.minecraftforge.installer.MirrorData.<clinit>(MirrorData.java:17)
    ... 11 more