They use the Apple TEE which they claim also protects GPU memory (I wasn't aware of this).

NVidia data center GPUs have a similar path, but not their consumer ones. Not sure about the NVidia Spark.

It's possible AMD Strix Halo can do this, but unlikely for any other PC based GPU environments.

Epyc has that VM encrypted memory thing, which comes pretty close. It does raise an interesting question, though: would a PCIe card passed through to a VM be able to DMA access the memory of neighboring devices?