I am not really familiar with the apple ecosystem, but my understanding is that they frown on open execution environments, that is emulators, virtual machines, interpreters etc. and a system that lets anyone develop and load games sounds like just that.
They haven’t allowed emulators till this year, but Xodot isn’t an emulator.
But what you’re likely thinking of with regards to execution is that they don’t allow creating new executable code. Ie no JIT or compilers, but interpreters are fine. Hence you can do GDScript (which runs in an interpreter like Python does) but you won’t be able to use the other language backends which compile down.
The Metal compiler is embedded in the Metal runtime and runtime compilation of GPU kernels is part of the official API. So I'm not sure if Apple would actually prohibit JIT-ing GPU code.
Now that I think of it, I wonder if you could create a Metal IDE using nothing more than the Swift Treesitter module and a Metal definition for it. As of today, you can use the Swift Playgrounds app if you don't mind not having any compiler errors or warnings provided to you.
Here’s one that might catch your fancy https://youtu.be/4TiBP0loC7s?si=HUNUSg0KMwRbdcK3