Apple releases iOS 13.4.1 & iPadOS 13.4.1 with FaceTime bug fix
At the same time that it is actively testing iOS 13.4.5, Apple has released iOS 13.4.1 and iPadOS 13.4.1, with minor fixes to the previous release on March 24.

Apple made the update to iOS 13.4 available on Tuesday afternoon at its normal release time. The update includes a fix for FaceTime calls made on a iOS 13.4 device not connecting to an iOS 9 or macOS El Capitan device, and other small bug fixes.
Other fixes include rectification of a bug with the Settings app where choosing Bluetooth from the quick actions menu on the Home screen would fail, and fixing an issue on the 12.9-inch iPad Pro (4th generation) and 11-inch iPad Pro (2nd generation) where the flashlight may not turn on after tapping the Flashlight button in Control Center or on the Lock screen.
Users can manually update their iPhone and iPad by accessing the Settings app then selecting General, then Software Update, followed by the option to install the update if it is made available to them.
Users with automatic updates enabled will be advised when the update has been downloaded to their device, with a notification informing it is ready to be installed.

Apple's iOS 13.4 brought iCloud folder sharing, full-fledged support for cursor and Bluetooth input peripherals like trackpads, and new Memoji stickers. Other changes include fixes to Mail, better VPN user interface notifications, and some changes to Music.

Apple made the update to iOS 13.4 available on Tuesday afternoon at its normal release time. The update includes a fix for FaceTime calls made on a iOS 13.4 device not connecting to an iOS 9 or macOS El Capitan device, and other small bug fixes.
Other fixes include rectification of a bug with the Settings app where choosing Bluetooth from the quick actions menu on the Home screen would fail, and fixing an issue on the 12.9-inch iPad Pro (4th generation) and 11-inch iPad Pro (2nd generation) where the flashlight may not turn on after tapping the Flashlight button in Control Center or on the Lock screen.
Users can manually update their iPhone and iPad by accessing the Settings app then selecting General, then Software Update, followed by the option to install the update if it is made available to them.
Users with automatic updates enabled will be advised when the update has been downloaded to their device, with a notification informing it is ready to be installed.

Apple's iOS 13.4 brought iCloud folder sharing, full-fledged support for cursor and Bluetooth input peripherals like trackpads, and new Memoji stickers. Other changes include fixes to Mail, better VPN user interface notifications, and some changes to Music.
Comments
A friend of mine facetimed me multiple times, and I was unable to answer the call no matter which one of my devices I tried to answer with. I was wondering what the hell was going on. No matter what I tried, it didn't work, no iPhone, no iPad no Mac, no whatever.
It now makes sense, because I know that my friend was using an old device with an old version of iOS on it, I think it was OS 9.
I'm glad an update is out already, because that was an annoying bug.
Bluetooth audio connections are an endless source of irritation.
Are they not sandboxed plugins?
I hope Apple patches the Screen Sharing issue. It’s very hard to help an older user.
The only thing I haven't tried is restoring from backup on iTunes. I'm not sure I want jump through those hoops. But it may be the only option. It'll be awhile before 13.4.5 is out an that may not fix it either. The 6.2 update doesn't appear to do a thing for the S2 line, but I'm tired of seeing the 6.2 Update Available every time I put my Watch on. I did report this to Apple Feedback but I expected to hear nothing, and my expectations were met.
Upgrading to 13.4.1 right now. Fingers crossed! (But expectations low)