Upon creating a new world for 1.16, I noticed immediately that there were no advancements. I created a new world without resource packs and data packs and still no advancements.

In the attached screenshot, it shows 1.16 in the top left corner and no advancements on screen.

Also attached is a screenshot of a 1.15.2 world loaded in 1.16 client which has the 1.16 advancements in the advancement menu.