I have tried to unlock the new 1.18 achievements on 2 worlds i have that were created before 1.18 and none of them worked on both worlds. it's been over 12 hours now and achievements are still locked.

Edit: I actually created a brand new 1.18 world and did some grinding untill i could try the "caves and cliffs" achievements. jumped from build limit down to -62 and survived. and did not get the achievement!