It’s all just debt. So when they got rid of the gold standard, we went from “this debt we have to you is secured by our stockpiles of gold” to “trust me bro, we won’t go bankrupt”. It would be the same with a CBDC.
Basically the digital Euro would be secured by the fact is if it wasn’t secured, the Eurozone would collapse, so states and the EU at large is interested in staying solvent.