Quick answer: hakuX 1.2.0, a free original Xbox emulator for Android, adds system link play between devices on the same network. Android Authority ran Halo 2 at full speed (30fps) on a Retroid Pocket G2 with a Turnip driver after the emulator's recent core rewrite.
hakuX, a free emulator that runs original Xbox games on Android, released version 1.2.0 on October 26. The big addition is system link: hakuX devices on the same Wi-Fi network find each other the way Xbox consoles did on a LAN. Devices on another subnet or behind a VPN like ZeroTier or Tailscale can be added by address. There's also XLink Kai support for system link over the internet.
Version 1.0.0 on October 23 replaced the old xemu/QEMU-based core: the Xbox's x86 code now runs through a FEX-based JIT, the Xbox kernel is reimplemented natively, and graphics are translated to Vulkan. Version 1.1.0 a day later added experimental support for Mali, Xclipse and PowerVR GPUs. The project says it's tuned for Adreno GPUs and can load custom Turnip drivers.
Android Authority tried the updated emulator on its handhelds. Halo 2 ran at full speed (30fps) on a Retroid Pocket G2 with a Turnip driver, while the system driver showed serious graphical glitches. It also ran well on the Anbernic RG 55G1, which uses the lower-end Snapdragon G1 Gen 2, and Project Gotham Racing 2 was playable on both. The developer listed Blood Wake, Burnout 3, Fable, MechAssault, Ninja Gaiden Black and Morrowind as running well on a Retroid Pocket 5 at 2x resolution, Android Authority reports.
Version 1.2.0 also fixes crashes in games including Silent Hill 2 and Doom 3, and cuts stutters when using Turnip.
hakuX needs an arm64 Android device with Vulkan. Its requirements say no BIOS, MCPX ROM or hard disk image is needed, it includes no copyrighted Xbox software, and it uses ISO or XISO images dumped from discs you own. The project also says hakuX is free and that its GitHub releases page is the only official download.