I have died at least three times now while carrying netherite weapons/tools. Each time, they despawned before I could collect them. (I don't need anyone judging me on how I keep dying. I haven't gotten my armor up to snuff with enchantments/netherite.)

I first died in lava in the nether. It took me about 60-90seconds to return to the location. They all despawned. Thankfully, there was a connection issue with Realms and it kicked me, resulting in it rewinding time and my items were back.

The second time I died was in my factory. I was digging in the ground to find a zombie, and there was an underwater cave. I ended up drowning. I was back at the spot within 10 seconds, and all my items had despawned. I dug all around in the walls, floor, and ceiling to see if they were hiding there. No such luck. Thankfully I had spare netherite weapons/tools.

The third time, I was spelunking and my health was low. An enderman got mad at me and killed me. I was back at the location within 30-60 seconds. Again, everything had despawned. At this point, I had to ask my friend (owner of the realm) to reset the world to an earlier save, because this is gettting ridiculous. 

All three times, my netherite weapons and tools -1 sword, 2 pickaxes, 1 axe, 1 shovel - (which have all been named) have despawned.