Basically, finish what I was doing here: GitHub - philipturner/ue5-nanite-macos: Nanite on macOS. I needed to replace some textures with buffers in the UE5 source code. Should be easy peasy for engine maintainers, but not myself because I’m not familiar with the code base. Hence why I personally couldn’t debug it in a reasonable amount of time, and gave up.
The rest is simply translating the Metal code here into HLSL and creating some Metal commands to deinterleave the two 32-bit halves into a full 64-bit word. Creating the Metal shader was the hardest part and that was done a year ago.