I was thinking of creating a retro style game for iOS using SpriteKit and I was wondering if there would be any way to run it on a Gameboy Advance.
Based on what I've seen, Gameboys can run any game written in any programming language as long as it "compiles to ARM Assembly". I checked if Swift compiles to ARM Assembly and there was a mention of Swift compiling to native code (i.e. assembly). Does this mean it would be possible to run a retro style iOS game on an actual Gameboy (keeping in mind the resolution the artwork would need to be and other such limitations)?
If there's any way I can create a game for iOS but have it run on a Gameboy Advance as well please let me know.
No. For a bunch of different reasons, the most important being SpriteKit would not be able to access any of the GameBoy Advance hardware.
It goes just beyond the Arm7 CPU. You need to work with the video registers and modes, which are all customized by nintendo.
You may be able to get swift to compile ARM7 code, but that is about as far as you are getting. The rest of the libs you will have to make yourself.