they've written a custom GPU framework to achieve the performance the level of performance they have. it's currently only compatible with macos, but is being ported to other operating systems.
It's not fundamentally incompatible, they just haven't written the code to make it compatible yet. GPU frameworks need a lot of OS specific code, so it will take some time for them to make it run perfectly on Linux.
My bad, I was referring to the new Linux implementation which is using Vulkan, which was not clear. The MacOS implementation only supports Metal, as MacOS does not support Vulkan natively. I assume the Vulkan implementation will also be what is used for the Windows build.
it will be released on both Linux and Windows, with Linux support currently being the top ranking issue on their GitHub page. they have a tracking issue showing that many pr's have already been merged working towards Linux support.