in the cmd puts me this 

G:\mine server 1.16.1\Nueva carpeta>java -Xmx4096M -Xms4096M -jar .jar nogui
2021-09-09 14:29:47,175 main WARN Advanced terminal features are not available in this environment
[14:29:47] [main/INFO] [cp.mo.mo.Launcher/MODLAUNCHER]: ModLauncher running: args [--gameDir, ., --launchTarget, fmlserver, --fml.forgeVersion, 36.2.4, --fml.mcpVersion, 20210115.111550, --fml.mcVersion, 1.16.5, --fml.forgeGroup, net.minecraftforge, nogui]
[14:29:47] [main/INFO] [cp.mo.mo.Launcher/MODLAUNCHER]: ModLauncher 8.0.9+86+master.3cf110c starting: java version 16.0.1 by Oracle Corporation
Exception in thread "main" java.lang.IllegalAccessError: class cpw.mods.modlauncher.SecureJarHandler (in unnamed module @0xca263c2) cannot access class sun.security.util.ManifestEntryVerifier (in module java.base) because module java.base does not export sun.security.util to unnamed module @0xca263c2
        at cpw.mods.modlauncher.SecureJarHandler.lambda$static$1(SecureJarHandler.java:41)
        at cpw.mods.modlauncher.api.LamdbaExceptionUtils.uncheck(LamdbaExceptionUtils.java:95)
        at cpw.mods.modlauncher.SecureJarHandler.<clinit>(SecureJarHandler.java:41)
        at cpw.mods.modlauncher.Launcher.lambda$new$6(Launcher.java:55)
        at java.base/java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1708)
        at cpw.mods.modlauncher.api.TypesafeMap.computeIfAbsent(TypesafeMap.java:52)
        at cpw.mods.modlauncher.api.TypesafeMap.computeIfAbsent(TypesafeMap.java:47)
        at cpw.mods.modlauncher.Environment.computePropertyIfAbsent(Environment.java:62)
        at cpw.mods.modlauncher.Launcher.<init>(Launcher.java:55)
        at cpw.mods.modlauncher.Launcher.main(Launcher.java:66)
        at net.minecraftforge.server.ServerMain$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)

Minecraft 1.16.5 requires Java 8 and you have Java 16.
Just downgrade.

On 9/9/2021 at 6:25 PM, uSkizzik said:

Minecraft 1.16.5 requires Java 8 and you have Java 16.
Just downgrade.

thx you sow much