How is that evidence that Apple ever tried to engage with Khronos on a Metal-like API, though?
Seeing as Apple had already stopped updating OpenGL versions about 4 years before the release of Metal, it seems more likely that Apple never planned on working with Khronos on anything.
Do a search for Apple & Khronos and you'll find a lot more examples of spats between them over the last decade than anything else. Including an ongoing legal dispute.
You also won't find any hint of involvement from Apple in anything Vulkan-related. Or really anything else Khronos-related. They've even pulled out of OpenCL - the thing that only Apple ever cared about in the first place.
No idea why they are still a member of the group. Possibly they just haven't been kicked out yet, possibly they still want to retain voting input for something (like webgl).
For the same reason Sony, Nintendo and Microsoft are, they care about specific parts of Khronos, not all of it, not for all their products.
Sony cares about Khronos on Android phones, not so much on Playstation.
Nintendo supports OpenGL 4.6 and Vulkan on the Switch, with NVN as the main API. During the previous generations they started to support GL like APIs, not really 1:1 to the standards.
Microsoft was the main contributor to the initial set of GlTF 2.0 improvements, and BabylonJS is the first browser engine to driver most of the WebGPU efforts, and they care about Khronos APIs in the context of WSL.
Apple once cared about Quickdraw 3D, OpenGL was the path out of the tiny market they were in and what NeXTSTEP used anyway, nowadays all relevant game engines support Metal anyway.
Seeing as Apple had already stopped updating OpenGL versions about 4 years before the release of Metal, it seems more likely that Apple never planned on working with Khronos on anything.