Username checks out, though I’m assuming you meant “demakes”?
Anyways, the demake I’m most familiar with is the in-progress Lego island. The YouTuber behind it documented part of the process in vlogs (linked on the GitHub page), so that might be an interesting starting point.
I hate to be nitpicky; but that's a decompilation, not a demake.
'Demake' usually refers to a game that gets remade for a system older (or less powerful) than the one it was released for. A good current example is the in-progress Super Mario 64 demake for GBA.
'Decompilation' is where one reverse-engineers a game (or any software!) back to its original source code, or close enough that when you build it, it's identical to an original copy. So, the goal of the Lego Island demake is to produce source code that can be built into a fully binary-compatible copy of Lego Island, indistinct from what's on the original CD.
Oh I don’t mind the nitpicking, thanks for the explanation! I (apparently erroneously) thought “demake” and “decompile” were synonyms. Guess I’m one of today’s 10000.
In that case the (now taken down, but forked a gazillion times) portal64 project would be a correct example of a demake, right?
I haven't checked it out yet, but I saw someone had made a Lumines demake for the gba. Usually I end up finding out about them through forums and youtube