Experience orbs' rendering is offset by +0.25 X compared to their actual position in the world. This is not a new bug; it has probably been in the game since the beginning. I just happened to determine it precisely while testing the new behavior of orbs in 1.16.100.

Steps to reproduce

1. Load the attached test world. It consists of a 5 x 5 x 5 chamber of barrier blocks with a 1-block empty space in the middle and two glass blocks for visual reference.
2. Press the button to summon an experience orb in the chamber.
3. Move side to side along the X and Z axes and observe the rendered position of the experience orb as you move across the coordinates of its chamber
4. Align your eye level with the floor of the orb chamber, and observer the orb's rendered Y position.

Expected results

The experience orb renders with the same alignment along each direction of each axis.

Actual results

The experience orb renders with the same alignment in the Y and Z directions. But on the X axis it is offset by about .25 block (4 pixels) in the + direction.

Note:

The X offset is more obvious if you set the xp_orb collision box to 0.0 width and 0.0 height. In that case it renders entirely outside its block in the +X direction. However, this is not a vanilla result so I did not include it in the test world.