This interview has some details about how it was done on Xbox: https://hanselminutes.com/632/eric-heutchy-on-backward-compatibility-xbox-one-x-enhanced-games-and-the-heutchy-method

This site has been a great source of news about all things retrogaming.
I support them on patreon now and hope they will make it through!

Some of their articles are a bit quirky, with the writing style suffering from occasional diversions which may even turn into rant or two. But I find this somewhat endearing rather than annoying. It conveys that they love doing what they’ve been doing.

I bought all the GBA FF games off eBay and only received counterfeit ones :-/ At least the ones I got don’t have batteries in them. Saving makes the games freeze for a small time but other than that they are working.

Completed the FF V GBA counterfeit on a DS lite. Ended up playing through the DS versions of III and IV, also off eBay, which do not seem to be fakes fortunately.