This crashes with the identical NSRangeException:

sandbox-exec -p '(version 1)(allow default)(deny iokit-open)'
python3 -c "import mlx.core"

This works fine (full IOKit access):

sandbox-exec -p '(version 1)(allow default)'
python3 -c "import mlx.core; print(mlx.core.default_device())"

TL;DR

Add an unrestricted IOKit rule to the danger-full-access sandbox template to allow Metal/GPU operations in child processes.

Guidance

• Verify that the crash occurs due to the Seatbelt sandbox profile restricting IOKit access by running the minimal reproduction command.
• Consider adding an unrestricted IOKit rule to the danger-full-access sandbox template: (allow iokit-open).
• Alternatively, use a scoped approach by adding specific IOKit registry entry classes: (allow iokit-open (iokit-registry-entry-class "AGXDeviceUserClient") (iokit-registry-entry-class "IOGPUDeviceUserClient")).
• Test the fix by running the reproduction command with the updated sandbox template.

Example

(allow iokit-open
  (iokit-registry-entry-class "RootDomainUserClient")
  (iokit-registry-entry-class "AGXDeviceUserClient")
  (iokit-registry-entry-class "IOGPUDeviceUserClient"))

Notes

The suggested fix assumes that granting unrestricted IOKit access is acceptable in danger-full-access mode. However, this may introduce security risks, and a more scoped approach may be preferred.

Recommendation

Apply the workaround by adding an unrestricted IOKit rule to the danger-full-access sandbox template, as it is the most straightforward solution to allow Metal/GPU operations in child processes.