Unity's inbuilt Level of Detail (LOD) system allows you to optimize your rendering by using low detail models for objects that are far away from the camera and only swapping to high detail when things come close.
The Official Tutorial explains how to use it and it has no direct interaction with animations so using it with Animancer is the same as any other system.
Using LODs for an animated character means having several copies of their model in the scene for the system to swap between. If they all have the same skeleton and you want to play the same animations on all of them, you can simply manage the animations normally for a single skeleton and use the SkinnedMeshRenderer.bones property to make the renderers of every LOD use that same set of animated bones instead of each LOD using its own copy of the skeleton.