The far lands existed beyond X/Z += 12,550,821 in Minecraft before beta 1.8. At that point, the terrain completely warps, resulting in a giant wall of stone with swiss cheese-like holes inside.
More details here: https://minecraft.wiki/w/Far_Lands
The far lands may be gone in Minecraft Java, but their legacy lives on. Through mods, they can be revived, and sometimes, they can exist in places you would never expect them to.