Is 1800 or 2100 max for weekly chest this week?

If you want an item level 226 piece of gear from The Great Vault next week, then you’ll need a Duelist rating (2100+). It is ONLY the Conquest gear upgrades that you make THIS WEEK that are capped at item level 220.

There are no caps on the Great Vault’s PvP considerations. Duelists (rank 5) or higher will receive item level 226 equipment from the Great Vault.
The First Week of Shadowlands Season 1 - Community / General Discussion - World of Warcraft Forums (blizzard.com)

Edit: Proper value!