Most desktop VR hardware currently available use Windows; because of this, the following instructions, and indeed most of this book will be a mixture of Windows installations and GearVR viewing. At the time of writing, Linux could be hacked to work with the HTC Vive and Oculus Rift, but it's a difficult road and a bit beyond the scope of this book. Apple PCs are just adding the capability to add an external video card for VR, as most of them simply do not have the video processing capability to render VR at the resolutions used by the Vive and Rift headsets.
React is, however, not PC specific. You could build all of the examples in this book with Linux or a Mac, and follow alongside, and use a Google Daydream, Unofficial Cardboard, or Samsung Gear VR to view all of the samples. In this case, some of the examples may use slightly different...