kunchboy

To anyone who comes across this and is wondering the same thing, I did some experimenting. I went onto my main world generated pre-1.21 and changed the landcover to 0.7 (previously 1). Ocean cover was set to 1, I didn't change that. Loading new chunks after changing gave mild terrain weirdness but no jagged chunk cutoffs like 1.20 if changing the landcover. So you are able to have oceans in previous worlds if you load new chunks after changing the settings with commands, and the chunks won't have odd cutoffs

EDIT
While exploring more, I DID come across some large chunk errors where the terrain will just cut off and not smoothly merge with old terrain. However, the above still stands. Most terrain seems to smooth and seems to do so more than 1.20.

Personally, I'm just going to make it part of my worlds lore. Strange things happen when you mess with timelines and time anyway. It almost makes sense to canon, lol.