I had a survival world starting on a island. But I was lucky enough to survive... had an amethyst geode connected to a ravine below my base... found moss blocks, dripstone, lots of materials and bamboo... So yeah, in the insane 1.18 update, I found a deep cave with a mineshaft. Then I found that the layer changes wasn't fully coded, because there was still the old lava layer. But I did not check everything for this evidence, because my world was already deleted. Wish I had better luck... and while I have not met this site yet, the evidence screenshot wasn't taken. Sorry Mojang!