After releasing iOS 13.3 last December 10, Apple has recently stopped signing version 13.2.3 of its operating system (and the respective version of iPadOS), putting an end to the possibility of downgrading.
The signature block on previous versions is a practice that Apple has been carrying on regularly for several years now. In addition to avoiding excessive fragmentation of the platform, ensuring that the largest number of users use the latest versions of the operating system, with this block we also try to keep the ecosystem more secure, preventing the use of firmware with vulnerabilities that allow to perform the jailbreak.
With iOS 13.3, we remember, a series of new features have arrived including a parental control tool called "Communication Limits" which blocks incoming and outgoing communications from anyone not in the contact list.
Apple, in recent days, has released the first beta version of iOS and iPadOS 13.3.1, of macOS 10.15.3, watchOS 6.1.2 and tvOS 13.3.1.