What are the differences between cryptocurrencies and digital currencies backed by CBs?
Two more differences 
(1) You can pay your taxes in a government controlled digital currency, and you can't do that in cryptocurrency.  According to Modern Monetary Theory, that is an essential element to the fundamental value of a currency
(2)  even though an individual cryptocurrency may have the feature of a limited supply, there's nothing to stop multiple cryptocurrencies being created, potentially diluting each other's value.  That is not the case with the single currency of the realm.