The animations for holding a loaded crossbow in first person view have been broken in 1.16.100. As shown, holding a loaded crossbow without an offhand item looks like you are holding the loaded crossbow with an offhand item. However, when you do hold an offhand item, it does not show in your offhand while holding a loaded crossbow, as seen in the screenshot with my Paper Doll holding a nautilus shell (happens to maps and arrows as well) in its offhand. Then here's the twist: holding a shield makes the loaded crossbow appear as if you weren't holding anything in your offhand, clipping through the shield.

Steps to Reproduce
1. Load a crossbow.
2. Hold it in your mainhand.
3. (for broken offhand animation) Hold any offhand item.

Expected Results:
The loaded crossbow (without offhand item) is located in the middle of the screen in first person view. With any offhand item, the crossbow is located to the left, and the offhand item renders, well, in the offhand.

Observed Results:
The loaded crossbow (without offhand item) is located to the left of the screen in first person view. With a shield in your offhand, the crossbow renders at the middle, clipping through the shield. With any other offhand item, that item simply does not render.