Probably the 4 BTC is sent to a change address which is part of your bitcoin address. You have nothing to be worried about. If you check your wallet, you will see the remaining 4 BTC on your wallet.
If it happens that you did not see your coins, import your seed phrase on Bluewallet wallet or Electrum. If you see your coins there, better to create a new wallet on the Bluewallet or Electrum and send the remaining coins there because blockchain.com wallet is close source.
Thank you! I read about change address, and am hoping that is the case, but I do not see my coins on the blockchain.com wallet. So to recover these funds, I should download electrum wallet and import my seed phrase? Is this safe?
Thank you so much.