At least on Boavista it hasn’t been possible for me to withdraw money neither from an ATM nor direct from the bank. As barely card payments are accepted here I couldn’t try this out.
In Sal I had no luck at all with vendor’s card payments - multiple failures. However, I did manage to get currency out from the ATM in my hotel.
Just got back from a week in Cape Verde. Didn’t have any problems on Sal, Sao Vincente, or Santo Antao with current account cards. Not many places take card, so it was mostly just ATM withdrawls, all of which charge you around £1.50/withdrawl, on top of the 3% foreign ATM withdrawl charge by Monzo (after the first £200).