Upon death, all worn items occasionally do not drop, but everything else does. For example, I died of kinetic energy in the nether flying in a tunnel, and everything in my inventory was safe at the death site, including my chestplate, but my elytra and the rest of my netherite armor was not there.

Steps to reproduce:

Create a creative world

equip armor

put some random items in your inventory

switch to survival and die a couple of times until your armor does not drop but the contents of your inventory does. Try in the nether as well.