Technically government cannot curb the usage of cryptos and I believe, Russian central bank also admitted the same few months back. So the only way left for government is to create fear among the crypto users of their country.
However, I don't see it happening in foreseeable future. While a lot of countries are discussing to implement CBDCs, only one country has started their trial run. So it's easier said than done!
That's the point. If governments unanimously agree on banning crypto usage worldwide in order to force the use of CBDCs, then crypto will be doomed. While it will still be possible to use crypto "under the table", the average person will be quite skeptical dealing with something that's declared as "illegal" by the government. By then, it may no longer be possible to buy/sell crypto against Fiat. Only direct crypto transactions between peers will be the norm in the crypto/Blockchain space.
With so many cryptocurrencies being largely dependent on centralized infrastructure (mostly centralized exchanges), it becomes so easy for a government to crackdown on crypto. In authoritarian governments (like China, and Venezuela), CBDCs will be enforced across the region. Since CBDCs will be "living" on the Blockchain, governments can see every single transaction and do with accounts as they please. It'll be the end of privacy as we speak, as everything lives on the digital realm.
Nonetheless, I believe that there's still a long way to go before considering CBDCs a real contender against traditional cryptocurrencies like Bitcoin and Ethereum. We may have to wait until governments launch their own CBDCs next year, in order to see how well they're adopted in the mainstream world. If people choose to deal with CBDCs more than crypto itself, then the latter will become largely unpopular. After all, CBDCs will gain the "same" features as crypto. Who would want to deal in crypto when you've got a CBDC with stable prices and all the good stuff of Blockchain? Time will tell us what lies ahead with the future of both CBDCs and crypto. Just my opinion