In fact, CBDC can be very dangerous for the value of a country's currency. Just imagine, even the uncontrolled circulation of fiat money can cause the value of that country's currency to experience a very drastic decline, while with CBDC, governments can freely create units of their country's CBDC continuously and it is very likely that the amount will be unlimited, however, if the government is unable to limit the circulation of their money, it will be dangerous for the future of their country's money. However, the story would be different if the Swiss government withdrew their fiat money and allowed their circulating CBDC to be used by citizens.
If uncontrolled circulation is bad, then I think they won't let this happen but maybe they are already doing some measures to prevent it and some of us only didn't know it yet up until now. IDK if that issue is the same to printing unlimited amounts of money but I'm sure they are not dumb enough to know its drawbacks especially they are assigned on that field.
But, maybe there are only other problems or causes on why the value of a country's currency can decline. Same goes with the CBDC. CBDC's are like a crypto because they run in the blockchain and again just like a crypto, they must have a limit when it comes to supply. I think they are backed with the country's available currency.