Apple just released 13.4.1 today for iOS and iPadOS and it fixes a number of bugs that people experienced in iOS 13.4.
Open Settings and go to General > Software Update to find it.
- Fixes an issue where devices running iPadOS 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.
- Addresses an issue on iPad Pro 12.9-inch (4th generation) and iPad Pro 11-inch (2nd generation) where the flashlight may not turn on after tapping the Flashlight button in Control Center or on the Lock screen.
- Addresses a bug with the Settings app where choosing Bluetooth from the quick actions menu on the Home screen would fail.