CBDC is pretty simple in concept. Money that is exclusively available digitally. There will be no difference, other than the lack of physical currency (i.e., banknotes). You cannot understand the difference when trading fiat with CBDC electronically; it'll be like trading national currencies via some Internet broker.

I don't understand how a CBDC can completely forbid its users from buying bitcoin, unless there has to be a justification for every transaction happening, which besides utopian is neither going to work in practice.