In the overworld it seems largely stone and endstone are the only things to generate on the surface. The generation of land beyond 1.17 loaded chunks changes significantly, a small stone wall generates on the edge of the new 1.18 chunks and cuts through the land till the void. Then generation of land from that point seems sparce (like the end... maybe) when land does generate the land is larger thicker and more rounded (like the end... maaaybee?)

P.S.(edit 1) in 1.17-1.18 structures just generate at y0 if they want idk why... odd though! It cut a door in half!

(edit 2) an island generated for the stronghold or rather stone just haphazzardly covered it, and diamonds generated with it... at y43! (or around there)

oh if you zoom on the stronghold image you can kind of see the diamonds

edit:3 cave roof's in the overworld on cave worlds seem to spawn netherrack and not bedrock on the new snapshot, also maybe a abundance of water at lower y levels? not sure on that. On updated worlds 1.17.1 to 21w43a in some case's it went bedrock then netherack for one chunk bedrock again then netherrack, lost my screenshots for that.

**edit 4: i was 10mill blocks out, wanted to know where the nearest stronghold was (floating island world) it said it was 0 blocks away.......  there was nothing but void around me, that stronghold was almost 10 million blocks away, I can't guess how that happened

Sorry for my spelling and grammer, hope this is helpful... and also sorry for dumping it all here.