All the examples across the internet try to pretend that every application is run on a single thread. There is no problem with synchronization, multithreading etc. Uncle Bob, in his "Clean Architecture" book mentions the topic but very briefly and suggests to postpone some decision as long as possible.
But real applications do not look like that. Even a very simple application (like "BuckPal" from "Get your hands dirty on Clean Architecture) should take it into account.
Let's say we have a bank
Account entity. In a use case we get an
Account object, withdraw some money and then save the account. And we are happy. No comment about synchronization, locking etc. In typical CRUD and DB framework centric application we usually use database transaction to synchronize access.
I don't see where all the stuff related to multithreading and synchronization should be put (there is a chance those are two different topics but I don't know).