It may make more sense if you split out the separate functions of money. In theory, money is 1) a medium of exchange, 2) a store of value, and 3) a unit of account (measure of value).
At the moment, GBP (and other hard currencies) serve remarkably well as a medium of exchange and measure of value - prices are (despite increasing inflation) quite stable; if you have £100 in your wallet, you’d have a pretty good idea what it’s worth and what you can buy with it, at least over the next few weeks. Moreover, GBP may preserve value in the short to medium term, but evidently not in the longer term, over a few years or decades. To some extent this is by design, as the money supply in a modern economy fluctuates with requirements (economic activity) and central bankers target price stability over value preservation.
Precious metals sit on the other side of that equation. They are not great as a medium of exchange, and there’s a degree of price volatility which make them difficult to use as a unit of account / measure of value. However, they tend to be good stores of value over long time periods.
Now, as I see it, if governments were to impose a CBDC, it would simply replace GBP in the above equation. Accordingly, if you were to opt out of the CBDC system, you’d be without an effective medium of exchange, equivalent to if you were trying to survive without cash or bank cards today. But if you hold precious metals, or any other hard assets, you’d still be preserving wealth. And one way or another you should be able to convert these into some form of medium of exchange to obtain goods and services, whether that be via a different currency or through straight barter. The immediate benefit of holding precious metals in this scenario is that you hold this value without any counterparty risk; i.e., you are not reliant on the permission of financial institutions or governments to realise the value of your metals.
My limited understanding of crypto is that it’s trying to be both a medium of exchange and a store of value at the same time. I’m not convinced this is possible in a modern economic system, but time will tell if it may end up as one or the other.