I have checked all of the silly and common mistakes such as wrong java version and incorrect run command. I have tried some earlier versions of java aswell like 16 and 15, still no luck.

Run: (sourced from the wiki)
java -Xmx8G -Xms8G -Dsun.rmi.dgc.server.gcInterval=2147483646 -XX:+UnlockExperimentalVMOptions -XX:G1NewSizePercent=0 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M -XX:+UseG1GC -jar forge-1.16.5-36.2.20.jar nogui

Logs

[06:32:54] [main/INFO] [cp.mo.mo.Launcher/MODLAUNCHER]: ModLauncher running: args [--gameDir, ., --launchTarget, fmlserver, --fml.forgeVersion, 36.2.20, --fml.mcpVersion, 20210115.111550, --fml.mcVersion, 1.16.5, --fml.forgeGroup, net.minecraftforge, nogui]
[06:32:54] [main/INFO] [cp.mo.mo.Launcher/MODLAUNCHER]: ModLauncher 8.0.9+86+master.3cf110c starting: java version 17.0.4 by Private Build
Exception in thread "main" java.lang.IllegalAccessError: class cpw.mods.modlauncher.SecureJarHandler (in unnamed module @0x594c619b) cannot access class sun.security.util.ManifestEntryVerifier (in module java.base) because module java.base does not export sun.security.util to unnamed module @0x594c619b
at cpw.mods.modlauncher.SecureJarHandler.lambda$static$1(SecureJarHandler.java:41)
at cpw.mods.modlauncher.api.LamdbaExceptionUtils.uncheck(LamdbaExceptionUtils.java:95)
at cpw.mods.modlauncher.SecureJarHandler.(SecureJarHandler.java:41)
at cpw.mods.modlauncher.Launcher.lambda$new$6(Launcher.java:55)
at java.base/java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1708)
at cpw.mods.modlauncher.api.TypesafeMap.computeIfAbsent(TypesafeMap.java:52)
at cpw.mods.modlauncher.api.TypesafeMap.computeIfAbsent(TypesafeMap.java:47)
at cpw.mods.modlauncher.Environment.computePropertyIfAbsent(Environment.java:62)
at cpw.mods.modlauncher.Launcher.(Launcher.java:55)
at cpw.mods.modlauncher.Launcher.main(Launcher.java:66)
at net.minecraftforge.server.ServerMain$Runner.runLauncher(ServerMain.java:63)
at net.minecraftforge.server.ServerMain$Runner.access$100(ServerMain.java:60)
at net.minecraftforge.server.ServerMain.main(ServerMain.java:57)

Any assistance is appreciated,
Thanks.

I needed to use a newer version of forge 1.16.5 and then use java 11 rather than 17.

I needed to use a newer version of forge 1.16.5 and then use java 11 rather than 17.

thx,it works