juste pour clore le sujet, voici la réponse que m’a donné le support Kraken…
"kraken is an exchange service, not a wallet service. So if you use your Kraken account as a wallet, it’s going to be more expensive for you than if you used a proper wallet like Trezor or Ledger Nano. Our withdrawal fees are about 4 USD, whereas the current transaction prices of Bitcoin are about 40 cents.
So I strongly recommend you do not use Kraken for daily transactions.
And yes, if the invoice for your basket is 0.0203828 XBT, you’ll need to withdraw 0.0203828 XBT + the 0.0005 XBT withdrawal fee"