Was able to get webGPU working without losing the sandbox (Sandboxed=true on chrome://gpu) by doing (agent output below):

1. Copy NVIDIA’s Vulkan manifest to a filename Chrome’s sandbox permits:

   sudo install -D -m 644 \
  /usr/share/vulkan/icd.d/nvidia_icd.x86_64.json \
  /etc/vulkan/icd.d/nvidia_icd.json

2. Launch Chrome with NVIDIA-only Vulkan enumeration and forced WebGPU interop:

   VK_DRIVER_FILES=/etc/vulkan/icd.d/nvidia_icd.json \
   google-chrome-stable \
  --ozone-platform=wayland \
  --enable-features=ForceEnableWebGpuInterop

And then now I just have my chrome launcher store that environment variable with the feature set via chrome://flags/#force-enable-webgpu-interop

(Note: running proprietary RPMFusion Nvidia drivers on Fedora KDE Wayland)