General Discussion

Check in PlayerTickEvent. If the player is not sneaking in Phase START and is sneaking in Phase END then they started sneaking. Make sure to check you are on the server, read the documentation that was linked to find out how.

The way you are attaching capabilities at the moment is for when the item is not owned by you (that is what AttachCapabilitiesEvent is for). For your own items, simply override initCapabilities.   You also need an ICapabilityProvider (the thing actually providing your capability).

Remove this whole stuff. ObfuscationReflectionHelper now remaps automatically. Simply call ObfuscationReflectionHelper.findField with the SRG name.   Names like this were reversed, the type is now at the end (FooEntity instead of EntityFoo).   Use ChunkManager#getTrackingPlayers instead of this custom method.   You have the wrong class here, this looks like it should be EffectInstance, not Effect.   You should never directly remove entities from the world. Use Entity#remove to remove an entity.   You need to learn Java.   Overall it very much looks like you are in over your head with these mods, if you cannot even figure out that EntityHanging has become HangingEntity.

It's not directly deprecated, but it has problems, such as the one given by Draco.

and how do i make it on server? sorry im pretty new to modding