In the US that's true. Here in 21st century Britain I can initiate a bank transfer to another person from my phone, and they can immediately spend that money.

But can you do that on a large scale?

In the UK yes. Their payment system is a long way ahead of that in the USA.

In fact, for much of the world, this "deposit a check" is definitely from last century. Instant transfer is reality in Europe, and even many countries in Africa and Asia operate mobile banking services where transfers happen right away.

The currency is not necessarily cryptocurrency; it can be "air-time".

https://en.wikipedia.org/wiki/M-Pesa

Here is a dirty little trick to make sure your check appears instantly in your account -- first you cash the check, then you deposit that cash to your account.