No new generation under old chunks

I might have undestood it wrong, but "New world generation is now inserted under existing chunks when upgrading a world to the new world height" doesn't mean that if I upgrade my old world to this version there would be new caves under the already generated chunks?
With bedrock turning into deepslate and all that?

I just made a copy of my world, it took a lot of time to load in, and nothing new under my base, neither the new caves or the "deepslate only mega block" under y=0