I never tested it but I could find world2minetest or alternatively:

Alternative 1 - OpenStreetMap + Real Terrain Mod

You could download heightmap from OpenStreetMap to use Real Terrain mod to generate it.

Alternative 2 - Use whatever tool to generate for Minecraft then convert from Minecraft into Luanti

You could use mcimport or MC2MT(Luanti forums thread)

I assume you ask where in the Git mention the Flathub link since Flathub deems it unverified? It’s on On Linux section of the ReadMe

Are there revese engineered open source version of the other games?