I installed PufferPanel, selected the forge template in setup, and configured a minecraft server (had no idea what i was doing lol) and then it gives me this error:
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)
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.minecraftforge.fml.relauncher.ServerLaunchWrapper.run(ServerLaunchWrapper.java:70)
at net.minecraftforge.fml.relauncher.ServerLaunchWrapper.main(ServerLaunchWrapper.java:34)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
... 6 more[DAEMON] Running post-execution steps
The problem is most likely due to a to recent version of Java, Forge 1.12.2 cannot be run on Java versions superior to Java 8.
Install Java 8 on your system and use it to start the server.
Here is the documentation page of PufferPanel that tells you how to handle multiple Java versions.