So I was trying to set up some 1.16 servers and as always I added -Xmx9216m to set more ram but when ever I launch the server it says something like "-X is unkown argument" but when removed - from -Xmx9216m it launches but I have no idea if it is working.
Did something changed in newer versions? It is first time I am setting 1.16 server, before I only set 1.12 and below servers...

I usually use this in my 1.12 servers: 

java.exe -jar server.jar -Xmx9216M -Xms4096M nogui

 But when I used it in my 1.16 server console showed this:

[17:07:28] [main/FATAL] [minecraft/Main]: Failed to start the minecraft server
joptsimple.UnrecognizedOptionException: x is not a recognized option
	at joptsimple.OptionException.unrecognizedOption(OptionException.java:108) ~[jopt-simple-5.0.4.jar:?] {}
	at joptsimple.OptionParser.validateOptionCharacters(OptionParser.java:633) ~[jopt-simple-5.0.4.jar:?] {}
	at joptsimple.OptionParser.handleShortOptionCluster(OptionParser.java:528) ~[jopt-simple-5.0.4.jar:?] {}
	at joptsimple.OptionParser.handleShortOptionToken(OptionParser.java:523) ~[jopt-simple-5.0.4.jar:?] {}
	at joptsimple.OptionParserState$2.handleArgument(OptionParserState.java:59) ~[jopt-simple-5.0.4.jar:?] {}
	at joptsimple.OptionParser.parse(OptionParser.java:396) ~[jopt-simple-5.0.4.jar:?] {}
	at net.minecraft.server.Main.main(Main.java:79) ~[?:?] {re:classloading}
	at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?] {}
	at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:?] {}
	at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?] {}
	at java.lang.reflect.Method.invoke(Method.java:564) ~[?:?] {}
	at net.minecraftforge.fml.loading.FMLServerLaunchProvider.lambda$launchService$0(FMLServerLaunchProvider.java:51) ~[server.jar:32.0] {}
	at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:37) [modlauncher-6.1.1.jar:?] {}
	at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:54) [modlauncher-6.1.1.jar:?] {}
	at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:72) [modlauncher-6.1.1.jar:?] {}
	at cpw.mods.modlauncher.Launcher.run(Launcher.java:81) [modlauncher-6.1.1.jar:?] {}
	at cpw.mods.modlauncher.Launcher.main(Launcher.java:65) [modlauncher-6.1.1.jar:?] {}
	at net.minecraftforge.server.ServerMain$Runner.runLauncher(ServerMain.java:63) [server.jar:?] {}
	at net.minecraftforge.server.ServerMain$Runner.access$100(ServerMain.java:60) [server.jar:?] {}
	at net.minecraftforge.server.ServerMain.main(ServerMain.java:57) [server.jar:?] {}

So I then I did this:
 

java -jar server.jar Xmx9216M Xms4096M nogui

And it launched, but I don't know if these Xmx and Xms are applied