CEX just means that the exchange is centralized, say owned by a company or group of people. There are CEXs that have KYC and CEXs that don't, like MEXC for example. A DEX is just a descentralized Exchange, doesn't have any owners.
I know the best way to start a CEX without AML and KYC is just to set the servers in a country which doesn't require AML/KYC, but it would be interesting to know if there is any specific country which allows this within the legality.