I’ve just got back from Sal in Cape Verde.
The Mastercard issue seems resolved. Everyone who takes Visa also takes Mastercard.
Most outlets have contactless terminals, however I found it a bit hit & miss. If contactless fails, chip & pin generally will work.
There are still many places that are cash only.
ATMs in Cape Verde appear to operate on the same network regardless of the bank (you’ll see the same 90s style graphic on the screen).
All ATMs charge a CVE250 fee per withdrawal, but WILL NOT tell you this. There is a DCC screen (which you should always decline), but no fee notification.