When i start a completely new Fabric server it will not get past the initial loading phase and crash instantly.
This is done on a server with 0 mods besides the aether and its required dependencies.
Fabric loader version: 0.11.6
Fabric API version: 0.36.0
The following error is displayed:

[11:53:35] [main/FATAL]: Failed to start the minecraft server
java.lang.RuntimeException: Could not execute entrypoint stage 'main' due to errors, provided by 'the_aether'!
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke0(EntrypointUtils.java:50) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke(EntrypointUtils.java:33) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointServer.start(EntrypointServer.java:33) ~[fabric-server-launch.jar:?]
at net.minecraft.server.Main.main(Main.java:92) [intermediary-server.jar:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78) ~[?:?]
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]
at java.lang.reflect.Method.invoke(Method.java:567) ~[?:?]
at net.fabricmc.loader.game.MinecraftGameProvider.launch(MinecraftGameProvider.java:234) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.knot.Knot.launch(Knot.java:153) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.knot.KnotServer.main(KnotServer.java:28) [fabric-server-launch.jar:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78) ~[?:?]
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]
at java.lang.reflect.Method.invoke(Method.java:567) ~[?:?]
at net.fabricmc.loader.launch.server.FabricServerLauncher.launch(FabricServerLauncher.java:68) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.server.FabricServerLauncher.setup(FabricServerLauncher.java:114) [fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.server.FabricServerLauncher.main(FabricServerLauncher.java:56) [fabric-server-launch.jar:?]
Caused by: java.lang.ExceptionInInitializerError
at com.aether.world.feature.AetherConfiguredFeatures.registerFeatures(AetherConfiguredFeatures.java:46) ~[aether-1.16.5-1.0.4.jar:?]
at com.aether.Aether.onInitialize(Aether.java:41) ~[aether-1.16.5-1.0.4.jar:?]
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke0(EntrypointUtils.java:47) ~[fabric-server-launch.jar:?]
... 17 more
Caused by: java.lang.RuntimeException: Cannot load class com.aether.util.DynamicBlockColorProvider in environment type SERVER
at net.fabricmc.loader.transformer.FabricTransformer.transform(FabricTransformer.java:78) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.knot.KnotClassDelegate.getPreMixinClassByteArray(KnotClassDelegate.java:191) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.knot.KnotClassDelegate.getPostMixinClassByteArray(KnotClassDelegate.java:156) ~[fabric-server-launch.jar:?]
at net.fabricmc.loader.launch.knot.KnotClassLoader.loadClass(KnotClassLoader.java:154) ~[fabric-server-launch.jar:?]
at java.lang.ClassLoader.loadClass(ClassLoader.java:519) ~[?:?]
at java.lang.ClassLoader.defineClass1(Native Method) ~[?:?]
at java.lang.ClassLoader.defineClass(ClassLoader.java:1010) ~[?:?]
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150) ~[?:?]
at net.fabricmc.loader.launch.knot.KnotClassLoader.loadClass(KnotClassLoader.java:170) ~[fabric-server-launch.jar:?]
at java.lang.ClassLoader.loadClass(ClassLoader.java:519) ~[?:?]
at com.aether.world.feature.AetherConfiguredFeatures$Configs.(AetherConfiguredFeatures.java:79) ~[aether-1.16.5-1.0.4.jar:?]
at com.aether.world.feature.AetherConfiguredFeatures.registerFeatures(AetherConfiguredFeatures.java:46) ~[aether-1.16.5-1.0.4.jar:?]
at com.aether.Aether.onInitialize(Aether.java:41) ~[aether-1.16.5-1.0.4.jar:?]
at net.fabricmc.loader.entrypoint.minecraft.hooks.EntrypointUtils.invoke0(EntrypointUtils.java:47) ~[fabric-server-launch.jar:?]
... 17 more

What version of Fabric API are you using?

The latest version in this case that is: 0.36.0.
Updated the original post with the loader and api version.

For the latest 1.16.5 version you need fabric API 0.33.x or lower. An update is coming out soon that should resolve this restriction

aha ill await that release :D thx for the info!