Need help. Minecraft Forge Server will not load. (Ubuntu 20.04 Desktop)

[The L2d]

Ok so I've been working on this for the past two day days and I can't seem to figure it out; (Also I'm running Ubuntu 20.04)
I've been following this tutorial https://www.linuxnorth.org/minecraft/modded_linux.html#Step 4 - Configure your new Modded Minecraft Server, and I can't get past step four.

I keep receiving this error when I try to load the forge-universal.jar (I renamed the file so I wouldn't have to retype the file every four seconds)
A problem occurred running the Server launcher.java.lang.reflect.InvocationTargetException
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:566)
        at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.run(ServerLaunchWrapper.java:70)
        at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.main(ServerLaunchWrapper.java:34)
Caused by: java.lang.ClassCastException: class jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to class java.net.URLClassLoader (jdk.internal.loader.ClassLoaders$AppClassLoader and java.net.URLClassLoader are in module java.base of loader 'bootstrap')
        at net.minecraft.launchwrapper.Launch.<init>(Launch.java:34)
        at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
        ... 6 more

I've tried reinstalling it, I've tried removing the files and redownloading it, I've tried just about everything that my smooth brain can do but I can't just seem to figure it out. I've looked at this github post thing and this looks like my best bet but honestly I'm not sure they even knew what they were talking about: https://github.com/MinecraftPortCentral/Cauldron-Issues/issues/26

 

I'm at my wits end and all I want to do is play Minecraft with my stupid friends... Send help!

[The L2d]

Ok so the problem was fixed, even though this may never see the light of day I do want to provide a fix in case someone on the internet has to fix this later on.
So the fix was as simple as switching to openjdk8, in order to do that you should enter the command sudo update-alternatives --config java just like so into your terminal of choice in linux and selecting 8.0.

Another possible fix was renaming it, although I never seemed to get it right and I'm not sure that was an actual fix.