Two weeks after the official release of iOS 13.4, Apple has recently made available a new minor update for iOS and iPadOS, which thus arrive at the version 13.4.1.
For more information on the news introduced with the latest operating systems, we refer you to reading the previous news, in this case there are no particular news except the resolution of some problems encountered by users. One of all, the inability to participate in video calls with Facetime, when the devices contacted were running iOS 9.3.6 or earlier, and OS X El Capitan 10.11.6 or earlier.
A problem that will certainly have affected few users, but which apparently has been solved with the new update. iOS / iPadOS 13.4.1 is already available for download for all compatible devices and the OTA notification should have arrived, otherwise it is possible to proceed manually from Settings> General> Software update.