In case of the banking system collapsing in a modern developed country? That’s such an extreme situation I’m not sure if holding cash would be the right hedge against it. That sounds more like a canned food and flour bags kind of time.

If a bank fails, the deposit insurance also fails and the government can’t step in either that will undercut the trust in all other banks too. I would expect a chain reaction of follow-on bank collapses and hyper-inflation.