https://wccftech.com/apple-is-no-longer-signing-ios-13-6-1-should-you-update/

Apple seeded iOS 13.7 last week to all users and today, the company has stopped signing iOS 13.6.1. What this means is that you can no longer downgrade to iOS 13.6.1 from iOS 13.7. iOS 13.7 adds one major feature to the fix - Exposure Notification Express system. However, if you're resting on iOS 13.6.1 and not sure if you want to update or not, here's what you should know.

As mentioned earlier, Apple introduced the Exposure Notification Express system with iOS 13.7 which will allow health authorities to release contact-tracing in their regions without having to develop an app. Authorities would simply have to enter a configuration file with their logo, name, and other details. Users will automatically get a notification when health authorities begin offering contact tracing.