Apple has released iOS 13.4.1 for the iPhone SE today. Ironically, anybody who pre-ordered their iPhone SE should be receiving them tomorrow, so you should expect the OS to be upgraded as you set it up.
iOS 13.4.1 was released for other iPhone models on April 7, 2020 and addressed an issue where devices running iOS 13.4 could not participate in FaceTime calls with devices running iOS 9.3.6 and earlier or OS X El Capitan 10.11.6 and earlier.
It also fixed a bug that prevented users from picking a Bluetooth device from the quick actions menu within Control Center.
If your software is not automatically upgraded to iOS 13.4.1 during setup tomorrow, you will be able to update your device to iOS 13.4.1 by navigating to Settings > General > Software Update.
