After Apple released updates for iOS 13.4 and iPad OS 13.4, it was reported that devices could not initiate FaceTime calls with other devices running legacy operating systems, especially iOS 9.3. 6 or OS X 10.11.6 El Capitan and earlier.
In response, the company released a patch introducing updates for iOS 13.4.1 and iPad OS 13.4.1. This update is not only a fix for the FaceTime error, but also an error in the application settings, which may cause Bluetooth to be selected from the Home menu's Quick Actions menu.
The iPadOS 13.4.1 also comes to address a bug that prevented the flashlight buttons on the Lock screen and in Control Center from working on the 4th-generation iPad Pro 12.9 inch and the 2nd-generation iPad Pro 11-inch. These updates are available over-the-air and you can check by going to Settings > General > Software Update to check for it.