Well that was fast....
Just got a new compile of monkey2 with a Sokol wrapper - and that deals with the basics of Apple Metal.
So, just running the base examples and the first 3 worked but the 4th failed. I worked it out to be the lack of a Metal shader, fixed it and it worked!!!!
And here's the result: Apple Metal!

Early days but looks like I've found a new toy... \o/