THIS IS A DATAPACK! You need to either add it to your world's datapack folder or use an automatic loader such as OpenLoader or Paxi.
This datapack makes Mythic Upgrades armors an upgrade from Advanced Netherite sets.
How to install?
Download the zip and put it in your world's datapacks folder.
Alternatively, install openloader or paxi, and put the datapack inside their data folder.