To get this achievement you will need:
-16 gold ingots
-16 Ancient Debris blocks
-Full set of diamond armor
How to get Ancient Debris blocks:
They spawn in the lower parts of the nether now. I just vein mined like you would in the overworld to get ore. If you aren't finding much it might be worth finding a soul sand valley biome because they are more common there. Though it will still take a while to get all the ancient debris that you need. (You need to mine ancient debris with a diamond pickaxe)
I'm gonna assume you know how to get the other items listed because they are all from previous minecraft versions.
Then once you have 16 ancient debris, just smelt the ancient debris in a furnace to make them into scraps. Then just craft them into 4 nether ingots.
4 scraps + 4 gold ingots = 1 netherite ingot
Then you should be able to use the ingots to upgrade your diamond armor into netherite using the smithing table.
Here is a video guide if anything I said was unclear: