AActorChannel is referenced on this page Networking Overview for Unreal Engine | Unreal Engine 5.1 Documentation
There is no such thing as AActorChannel.
There is however UActorChannel.
I’ve seen other references to AActorChannel on the forum so this is confusing.
https://.unrealengine.com/showthread.php?59275-Replicating-TArrays-crashes-game&p=231425#post231425
It looks to have been UActorChannel in the codebase all the way back to 4.0 though.
https://github.com/EpicGames/UnrealEngine/blob/4.0/Engine/Source/Runtime/Engine/Classes/Engine/ActorChannel.h