Without the official Minecraft server .JAR, Fabric Loader cannot launch.
Exception in thread "main" java.lang.RuntimeException: Failed to setup Fabric server environment!
at net.fabricmc.loader.launch.server.FabricServerLauncher.main(FabricServerLauncher.java:58)
Caused by: java.lang.RuntimeException: Searched for 'server.jar' but could not find it.
at net.fabricmc.loader.launch.server.FabricServerLauncher.setup(FabricServerLauncher.java:106)
at net.fabricmc.loader.launch.server.FabricServerLauncher.main(FabricServerLauncher.java:56)