Let’s begin with a definition of terms.
XR Plug-in Management: This package facilitates the Unity XR lifecycle and allows you to enable XR support for various platforms such as Android, iOS, and the Universal Windows Platform. Its code has nothing to do with OpenXR.
OpenXR Plug-in: This package “plugs in” to XR Plug-in Management, and enables your Unity app to run on OpenXR runtimes. When this package is installed, you see an OpenXR checkbox in XR Plug-in Management.
Unity OpenXR: Meta: This package depends on both the OpenXR Plug-in and AR Foundation. It builds on the base functionality of the OpenXR Plug-in, allowing you to build AR Foundation apps for the Meta Quest OpenXR runtime. It defines AR Foundation subsystem implementations for various AR features as explained in its documentation.
With this cleared up, we can answer your questions.
Exactly. Unity OpenXR: Meta is one of many implementations of AR Foundation. When you build an app with AR Foundation, you enable yourself to deploy to ARCore, ARKit, visionOS, Meta Quest, HoloLens, and other platforms as explained in the AR Foundation manual.
For this reason, our first priorities with this package have been to enable support for features that are also available on other platforms, allowing AR Foundation users to port their apps to various different platforms.
Unity OpenXR: Meta does not integrate passthrough mesh projection, but Meta’s OpenXR runtime (C++ code that you don’t have access to in Unity) is capable of this feature.
To access passthrough mesh projection in Unity today, you would need to use some other plug-in entirely, potentially replacing both Unity OpenXR: Meta and the OpenXR Plug-in in your project. There may be a solution for this in the Meta Quest Developer Hub, which is where you should start for advanced Meta-specific features.
It may be possible to mix and match Meta Quest Developer Hub solutions along with our Unity OpenXR: Meta package. I don’t know, and we don’t test this, so I can’t advise you. But it may be possible. Otherwise your options are to use a Meta Quest-specific solution such as Meta Quest Developer Hub, or make a feature request that we support passthrough mesh projection in the Unity OpenXR: Meta package.