How does this work? Does it run the x86_64 version of Wine in Box64? My understanding of wine was that it just translates API calls, shouldn't it work on any ISA then? (Or is most of a program / game math and that stuff would fail?)
Box64 does the x64 to ARM translation (while keeping performance as high as possible by calling native ARM library code wherever possible). Throw Wine in there to implement the Windows APIs and you can run amd64 PE binaries on aarch64 with decent performance.
You can't run amd64 without something like Box64 because Wine is not an emulator, so it doesn't interpret or rewrite the instructions to aarch64.
You can use Box64 on other ISAs if you implement the necessary translation code. I believe this is what's being done to run games on RISC-V, but I'm not 100% sure. Good ol' qemu-static would also do the job if Box64 isn't compatible (yet), but that's running the entire application in a foreign architecture so the overhead would be a lot more significant.
Wine doesn't do any of that as far as I know. It loads a Windows PE file, it's (placeholder) DLL dependencies, and starts executing at the main entrypoint. Box64 does translation and has some specific placeholder DLLs that intercept API calls and call native code rather than emulating the entire process.
If what you describe is being done, it's being done by Box64. I don't know enough about aarch64 to know what ARM64X and ARM64EC do, though. I can find [a Github comment](https://github.com/ptitSeb/box64/pull/858#issuecomment-16057...) where one of the authors states that the goal is to implement ARM64EC, but I wouldn't know what the status is on that.
Wine does support ARM64EC and I'm pretty sure you can actually use an x86 emulator with it too (at the very least Hangover should support this, minimizing the amount of emulated code needed.)
