A) Banks seem to be getting out of the business of hosting deposit boxes. I’d guess it’s not worth the hassle and liability.

B) I don’t know about all of them, but the ones I’ve used have explicit rules against storing cash.

Would a so-called cbdc work? Get a bank account at the Fed that only gives you overnight rates (i.e. low but still higher than banks!), and only risk is sovereign risk.

Akin to the narrow banks proposals of a few years ago

Given that the Fed refused to grant licenses to those narrow banks, with no real justification, those CBDCs seem unlikely to happen.