This is simply not true. In South Africa, one of the largest African economies, you cannot hold foreign currency unless you are traveling and then you have to sell it back within 30 days of returning to the country. You can open a foreign currency account with a minimum of eg R1500 which is half the monthly minimum wage. Then there are the exchange fees to talk about. You are oversimplifying.
So having foreign currency in stable coins is allowed in South Africa?
iirc isn't the whole point of crypto that no one knows what you have or what you do with it?
They know even less with cash!
Crypto is not as reliably anonymous as cash. Anything with a distributed ledger is pseudonymous so if one transaction can on your wallet can be linked to you, so can all other transactions, including historical ones, to that wallet.