https://www.fiscal.treasury.gov/ach/ and https://www.swift.com handle much of the US, and it's a system developed in the 70s (or earlier) and it works.
It could be modernized and things like https://explore.fednow.org are trying to do that.
But the problems involved are not things a blockchain would secure because there's a trusted intermediary which can just run a database.
https://www.fiscal.treasury.gov/ach/ and https://www.swift.com handle much of the US, and it's a system developed in the 70s (or earlier) and it works.
It could be modernized and things like https://explore.fednow.org are trying to do that.
But the problems involved are not things a blockchain would secure because there's a trusted intermediary which can just run a database.