This release seems to be aimed at fixing minor bugs within iOS and iPadOS 13.3.

Another week, another iOS beta bugfix release. The staggered and piecemeal release of iOS 13 has been anything but smooth. When iOS 13.3 was released, we thought Apple might be done fixing bugs and adding features for awhile (at least until the new year). But lo and behold, the beta releases of iOS and iPadOS 13.3.1 have begun.
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https://www.macworld.com/article/3505940/ios-and-ipados-1331-features-release-date-beta-how-to-install.html