Cycles: Select Metal compute device by default on Apple Silicon machines

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Pull Request: https://projects.blender.org/blender/blender/pulls/121672

intern/cycles/blender/addon/properties.py

@@ -1452,6 +1452,14 @@ class CyclesDeviceSettings(bpy.types.PropertyGroup):
 class CyclesPreferences(bpy.types.AddonPreferences):
     bl_idname = __package__
 
+    def default_device():
+        import platform
+        # Default to selecting the Metal compute device on Apple Silicon GPUs
+        # (drivers are tightly integrated with macOS so pose no stability risk)
+        if (platform.system() == 'Darwin') and (platform.machine() == 'arm64'):
+            return 5
+        return 0
+
     def get_device_types(self, context):
         import _cycles
         has_cuda, has_optix, has_hip, has_metal, has_oneapi, has_hiprt = _cycles.get_device_types()
@@ -1473,6 +1481,7 @@ class CyclesPreferences(bpy.types.AddonPreferences):
     compute_device_type: EnumProperty(
         name="Compute Device Type",
         description="Device to use for computation (rendering with Cycles)",
+        default=CyclesPreferences.default_device(),
         items=CyclesPreferences.get_device_types,
     )