What is an asynchronous programming in terms of c#?

GetAllData method is used to manage the asynchronous execution flow of both methods.
It's worth noting that this optimization should only be applied in cases where the returned result from the asynchronous method is not required. If the result is required, then returning Task is necessary to return the result.

Hold on, can you explain ConfigureAwait(true/false) more deeply?

Certainly!
The ConfigureAwait method is used to configure how an async method continues after an awaited operation completes. It has a single boolean parameter, continueOnCapturedContext, which specifies whether the continuation should occur on the captured context or not.
The captured context refers to the current synchronization context, which is usually the current thread's execution context. When ConfigureAwait is called with a parameter of true, it means that the continuation should execute on the captured context (i.e., the current thread). When called with a parameter of false, it means that the continuation should execute on any available thread from the thread pool.
Here's a more detailed explanation of how ConfigureAwait works:
When an await expression is encountered in an async method, the compiler generates code that creates a state machine to manage the execution of the method. The state machine executes the code up to the await expression and then suspends the execution of the method until the awaited operation completes.
When the awaited operation completes, the state machine resumes the execution of the method, but it needs to decide whether to execute the continuation on the captured context or not. If ConfigureAwait was called with a parameter of true, the continuation will be executed on the captured context (usually the current thread). If ConfigureAwait was called with a parameter of false, the continuation will be executed on any available thread from the thread pool.
The decision of whether to use