This actually affects 20w18a, but who cares anyways.

Before 1.16 snapshots: Overworld superflat preset is normal; it has trees, lakes, mineshafts, villages, etc.

Now: Random structures appear all over the world, even when the biome isn't correct. With the normal overworld preset, it's a plains biome. But you can find a desert temple, jungle temple, ocean ruin, shipwreck, witch hut, and even igloo. Even though u can see them, if you do /locate shipwreck for example, it says, "Cannot find structure within a reasonable distance", even if you can see it right in front of your eyes!!!