The updates do not stop on iOS, an example is that yesterday we already had iOS 13.2.2 which is said soon. With this, what Apple intends is to solve a series of problems that iOS has been dragging on the fly, for not having designed it as the company's canons command from the beginning. This latest version fixes problems about RAM memory management and automatic closing of applications. Now Apple has stopped signing iOS 13.1.3 so you will not be able to downgrade from any version of iOS 13.2, that firmware has definitely passed away.
It is true that the news may not seem too interesting, but very often, especially in those who enjoy older devices, there are errors at the performance level that cause serious damage to users with certain updates, this is the reason why the whate Apple continues to sign earlier versions of iOS, and the reason why users carry out this downgrade which amounts to downloading the iOS version. The problem, of course, is that Apple verifies the iOS version and the signature over the internet so that it can be executed, that is, when an iOS version is not signed, it is impossible to install it in a traditional way on our iPhone.
Now Apple has deprecated iOS 13.1.3 and stopped signing it, so you will not be able to go back if you are running iOS 13.2 or any of its later versions. The time has come to get used to it, although I recommend as always to keep the iPhone updated to the latest version available in order to avoid possible security flaws that put not only our data at risk, but also the data of our relatives that we have in our iOS device on duty.