How it works: HaloPad runs the original haloce.exe (Custom Edition 1.10), a 32-bit x86 Windows binary. On your Mac, a static translator turns its x86 code into native ARM64 ahead of time. Nothing is compiled on the device while you play, so it needs no JIT, which iOS doesn't allow.
Around that code sits a runtime built for this one game, not a general Windows layer. It stands in for the Windows services the game calls. Direct3D 9 runs on Metal, and all 804 of Halo's shaders are translated to Metal and checked against a reference interpreter.
DirectInput maps to touch and game controllers, and Winsock runs on native sockets. Audio, files and the registry are handled too. The game's own multiplayer chat DLLs are translated and loaded the same way.
Online works because nothing in the netcode was rewritten. It's Halo PC's own networking, doing the same server handshake and pulling the same server list from the community master server. To a server, an iPad looks like any other PC client.
Opus and Astra were instrumental in getting the build to this point. Enjoy.