My understanding is that MacRuby relied on Apple's ill-fated attempts to migrate from reference counting to regular garbage collection. I would be surprised if GC still worked on modern arm64 macOS. RubyMotion later adopted ARC but then it's not really Ruby anymore.
I dropped OSX long ago, so can't even try it out any more.
I wonder how much of the LLVM bits could be reused? I'm sure LLVM's changed a bunch in the last 15 years, too.