Motion controller inputs and tracking are supported by the built-in OpenXR plugin, so Varjo OpenXR plugin is not required to enable controllers in Unreal.
Virtual Reality Template is a good starting point for a project with motion controllers. If you use
Virtual Reality Template, please note that in Unreal Engine 4.26 the template is still built for SteamVR. You can just remove the SteamVR specific parts from the blueprints. A completely new VR template designed for OpenXR will be available for Unreal Engine 4.27.
Varjo OpenXR runtime currently support Vive and Index controller input mappings. You bind action mappings for these in Project Settings > Input > Bindings.
Refer to Unreal Engine documentation for more information on how to set up and use the motion controllers.