Well technically...

[1] - "How Mainframes Keep The Financial Industry Up And Running"

"...92 of the top 100 banks use the mainframe to provide banking services to customers, and other types of financial services companies depend on the mainframe, as well. Visa, for example, uses the mainframe to process billions of credit and debit card payments every year. According to some estimates, up to $3 trillion in daily commerce flows through mainframes..."

[1] https://blog.share.org/Article/mainframe-matters-how-mainfra...

Technically technically, you're feeding data into a system whose purpose is the care and feeding of a mainframe. That veneer is pretty thin in places and so it tends to feel like you're talking to a mainframe even when you're talking to an arbitrator for the mainframe.

Oh I see...you are here for an argument... https://youtu.be/ohDB5gbtaEQ

Shut your festering gob, you tit! Your type makes me puke! You vacuous, toffee-nosed malodorous pervert!

I am sorry, but I am not allowed to argue on my free time... :-)

You basically are.

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.