In 1.16.5, the player looks like there is a light source above them in the survival inventory. However, in 21w10a, it now appears that the light source is below them. This doesn't make as much sense to have a light source from below.
- Open your survival inventory in 21w10a
→ Notice how there is ambient occlusion (shadow) on the top of your player's head
- Open your survival inventory in 1.16.5
→ Notice how there is no ambient occlusion on top of your player's head