Now imagine ECB launching CBDC and making a smart contract that forbids your wallet from sending money to well-known CEXes like Coinbase, Binance, Kraken etc.
Good. So that means we'll have an abrupt rise in peer-to-peer exchanges like Bisq. Again, there is no way to stop me from buying bitcoin, unless you enforce me to justify every transaction I make, and even that way, you can't know I'm lying.
Of course people will be ingenious to find other -roundabout- solutions: I can buy a highly-sought product (let's say a PS5 or an iPhone*) with CBDC and then sell it in the black market for BTC.
That's very roundabout. Just sell it peer-to-peer, and you can even select a premium price. In fact, I have never sold bitcoin without a premium price once. I'm regularly charging an extra 5% whenever I'm not in hurry, and a 2% when I'm in hurry. People buy those.