Answered here: Burned token still visible on opensea and manifold studio
If it’s owned by the Null Address it has already been burned. You’re seeing the large amount because it’s owned by the burn wallet. If you would like Opensea to hide this token, like it’s described in the thread you’ll need to reach out to their support. Deleting the collection Opensea doesn’t burn anything it just hides the contract from Opensea.