MC-213802 – Copper is not upgraded correctly from pre-21w05a worlds
Get the Snapshot
Snapshots are available for Minecraft Java Edition. To install the snapshot, open up the Minecraft Launcher and enable snapshots in the "Installations" tab.
Testing versions can corrupt your world, please backup and/or run them in a different folder from your main worlds.
If you want to know what else is being added and changed in the Caves & Cliffs update, check out the previous snapshot post. For the latest news about the Nether Update, see the previous release post.