TotalSegmentator appears to have added the option for MPS where your Mac Pro AMD Radeon Pro Vega II card supports the mps backend for PyTorch.
It does seem to be a bit on the untested and new side as the following place in the readme hasn’t been updated to reflect the mps option although you can see that --device does allow the “mps” option.
The SlicerTotalSegmentator utilizes the TotalSegmentator python package, but will need to be updated to handle the MPS option as right now if it doesn’t detect a CUDA compatible GPU it will use CPU. See the following code that would need to be updated.
It appears that the MPS backend for PyTorch originally came out for PyTorch 2 with fixes and improvements over time. Since you are on an Intel Mac, you will be stuck on PyTorch 2.2.x as the latest since developers dropped support for it and were instead only going to support macOS on Apple Silicon.
Would you be willing to complete the code changes for SlicerTotalSegmentator and update the documentation for the TotalSegmentator package for your MPS use case? A majority of Slicer users are on Windows, so there has been less of a need for macOS specific tasks. Alternatively, a Windows machine with a CUDA enabled driver would be the easiest environment to immediately begin using.