Are all operations added to MainQueue necessarily executed on the main thread?

Not necessarily. Operations added to the MainQueue (main queue) in iOS are executed on the main thread if they are specifically added to the main queue via DispatchQueue.main.

However, if operations are added to other queues (for example, global or custom queues), they may be executed on a background thread.

It is important to understand that only tasks dispatched to DispatchQueue.main are guaranteed to be executed on the main thread, which is responsible for updating the UI and handling user events.