Apple has released iOS and iPadOS 13.4.1. This is a small bugfix release; it wasn’t ever even released as a public or developer beta.
The update fixes a glitch whereby users were having trouble connecting in FaceTime calls with devices running very old versions of iOS or macOS.
The release notes for iOS are as follows:
Fixes 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.
Addresses a bug with the Settings app where choosing Bluetooth from the quick actions menu on the Home screen would fail.
The iPadOS release features the same release notes, with the following additional item:
The next significant release is iOS and iPadOS 13.4.5, which is currently in beta testing.