This is the first release of gba-llvm-devkit for Linux and macOS arm64. Hopefully it somewhat works.
See README.md file in the root of this repo or the root of the package for what should work and how it should work.
The Linux packages indicate on what distro they were built. If your distro+version isn't one of these, I'd give the package for your architecture a try anyways. The tar is just a packed up folder structure.
If things don't work for you, try building from source. The process isn't too involved.
Building for macOS x86_64 should just work.
Windows isn't supported in this first release.