Thanks for the answers.
I created a (live) Share dealing account and set currency conversion to Manual, as suggested.
I have a couple of additional questions.
As a UK tax resident, the account base currency is GBP. Is it possible to change it to EUR?
I would like to be able to deposit AND withdraw in EUR and USD, from my accounts in these currencies. It's all clear for deposits. For withdrawals, I see I can only add the details of a single bank account. Does it imply I will be only able to withdraw to that account? If so, does it mean I can either withdraw to my EUR or USD account, not both?
Related to the previous question: if I can only withdraw to a single registered account, in future will I be able to change the bank details to a different account, make a withdrawal in the other currency, and then change it again to the initial account? I understand this may imply a delay for the verification of the accounts, but I am not expecting to withdraw USD frequently and this would be acceptable for me.