I'm confused how this can exist. It's a blatant ripoff of Minecraft, including fonts, assets, color schemes, etc. Call it a re-implementation all you like (I doubt it given Minecraft is Java and easy to decompile, and this is also JVM) but I don't see how that would fly.

If I decompile a commercial game, use GPT to rewrite the decompiled code and maybe change the assets a bit, can I just release that as open source?