Have you had experience developing or working with multi-threaded applications?

Yes, I have experience developing multithreaded applications. In iOS, GCD (Grand Central Dispatch) and OperationQueue are usually used for this.

For example, GCD can be used to perform tasks in the background thread to avoid blocking the UI:

DispatchQueue.global(qos: .background).async {
    // Long operation
    let result = heavyCalculation()
    DispatchQueue.main.async {
        // UI update
        self.label.text = "Result: \(result)"
    }
}

I have also dealt with data synchronization between threads, using semaphores and locks to prevent data races.