I am sad to say that I have failed to make SteamVR Input work with Unity XR. This consequence is that I need to re-implement the OpenVR support which worked in Unity versions before Unity XR. This will take some time to do well, but I strive to release Humanoid Control v3.4 with full support for OpenVR in Unity 2020+ as soon as possible.
It was already known that Unity XR and SteamVR did not work nicely together. Valve already made clear that they were “unable to find a good compromise between Unity Input System and OpenVR”. Nevertheless I hoped to find a way to support OpenVR input besides Unity XR tracking. However, I recently found out that when Unity XR is used, all input from the OpenVR action manifests is somehow disabled. The same is true the other way round: when you start to use OpenVR action manifests, Unity XR input is not longer returning values. So it is simply not possible to use the two together.
So the strategy now is to re-implement the OpenVR support I have for Unity 2019.4 and earlier for Unity 2020.1 and higher. This also means that you will probably need to choose between using Unity XR and OpenVR and that it is likely that having one binary which works fully for all platforms is no longer an option.
The way out of here seems to be OpenXR. Humanoid Control does work with OpenXR in Unity XR mode, including input from OpenVR. However, this path is also still very unclear to me: will Vive Trackers be supported, what about skeletal tracking and especially: how? So for now my expectations are quite low seeing the progress with Unity XR in the past year.
So to conclude, my focus will now be on adding OpenVR support to Humanoid Control with Unity 2020+ again as soon as possible. This also means that the development of Humanoid Control 4 will be paused for the moment until this issue has been resolved.