If you have a Unity 2018 project, you should consider planning for a migration forward to Unity 2020.3 LTS and the Mixed Reality OpenXR plugin. Unity 2018.4 LTS has reached the end of Unity's two-year Long-Term Support window and is no longer receiving updates from Unity, although your projects will continue to run. If you have multiple Office products you may have to scroll through the list of your owned products, or if you have an Microsoft 365 subscription, in the header, select Services and subscriptions which lists all the Microsoft products you own. From the Office home page select Install Office. The OpenXR plugin is the only path for mixed reality development in Unity 2021.2 and later, as the final Unity version to support the Windows XR plugin was Unity 2021.1. Project (Standard or Professional) Non-subscription version. If you are trying out early Unity 2021.2 builds, get started with the Mixed Reality OpenXR plugin. If you are developing apps for HoloLens (1st gen), these headsets remain supported in Unity 2019 LTS with Legacy Built-in XR for the full lifecycle of Unity 2019 LTS through mid-2022. In Unity 2020, Azure Spatial Anchors is supported within the XR Plug-in framework. While Unity 2019 does offer a new XR Plug-in framework, Microsoft is not currently recommending that path in Unity 2019 due to Azure Spatial Anchors incompatibilities with AR Foundation 2.

Unity has deprecated its Legacy Built-in XR support as of Unity 2019.

How to install project reality