They could just use Wine (Software) I suppose.

It's how I have been playing since 2010 on Linux. No Windows needed.

It's also how they do it for FFX|V for the macOS I believe, though via using a proprietary fork, which raises a fun(?) issue when running via Wine: It sees you are doing that, so it decides you are running it on macOS and so you need to have bought the game for macOS to be able to log in, unless you hide the fact that you are running it via Wine...

Wine (Software) also runs things on arm machines by the by, and seeing how poorly new Windows thingies support old Windows thingies... perhaps that's the way to go?