Asynchronous read in CoreData - Difference in using newBackgroundContext + FetchRequest vs newBackgroundContext + NSAsynchronousFetchRequest?

It seems there are 2 ways to perform asynchronous read in CoreData, without blocking main thread UI.

newBackgroundContext + FetchRequest

Source : https://www.advancedswift.com/core-data-background-fetch-save-create/

// Create a new background managed object context
let context = persistentContainer.newBackgroundContext()

// If needed, ensure the background context stays
// up to date with changes from the parent
context.automaticallyMergesChangesFromParent = true

// Perform operations on the background context
// asynchronously
context.perform {
    do {
        // Create a fetch request
        let fetchRequest: NSFetchRequest<CustomEntity>

        fetchRequest = CustomEntity.fetchRequest()
        fetchRequest.fetchLimit = 1

        let objects = try context.fetch(fetchRequest)

        // Handle fetched objects
    }
    catch let error {
        // Handle error
    }
}

newBackgroundContext + NSAsynchronousFetchRequest

Source: https://www.marcosantadev.com/coredata_crud_concurrency_swift_2/

let privateManagedObjectContext = persistentContainer.newBackgroundContext()

// Creates a fetch request to get all the dogs saved
let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Dog")

// Creates `asynchronousFetchRequest` with the fetch request and the completion closure
let asynchronousFetchRequest = NSAsynchronousFetchRequest(fetchRequest: fetchRequest) { asynchronousFetchResult in

    // Retrieves an array of dogs from the fetch result `finalResult`
    guard let result = asynchronousFetchResult.finalResult as? [Dog] else { return }

    // Dispatches to use the data in the main queue
    DispatchQueue.main.async {
        // Do something
    }
}

do {
    // Executes `asynchronousFetchRequest`
    try privateManagedObjectContext.execute(asynchronousFetchRequest)
} catch let error {
    print("NSAsynchronousFetchRequest error: \(error)")
}

However, note that, the above code will unfortunately cause fatal error, if I were to enable flag -com.apple.CoreData.ConcurrencyDebug 1.

So far, I do not have a good solution to such. For more detail, please refer to https://developer.apple.com/forums/thread/697718 ?

May I know, what is the difference among newBackgroundContext + FetchRequest vs newBackgroundContext + NSAsynchronousFetchRequest? How should I choose one over another? Thank you.