https://wccftech.com/apple-stops-signing-ios-13-4-heres-what-you-need-to-know/

Last week, Apple saw fit to release its latest iOS 13.4.1 software update for the iPhone and iPad. Now, the company has stopped signing iOS 13.4 which means that it is no longer possible to downgrade to it from iOS 13.4.1. If you're an average iPhone user, the news might not be of good value to you. If you're a bit tech-savvy and interested in jailbreaking your iPhone or iPad, the news of Apple not signing the previous iOS build will entice you.

Take note that iOS 13.4.1 was a minor update pertaining to the number of features that it brought to the table. It fixed the Bluetooth and FaceTime issues which were brought forward by iOS 13.4. So if you're someone who is not familiar with the jailbreak, Apple's decision to stop signing iOS 13.4 is not a big deal. Even if you tend to jailbreak your iPhone, you don't have to rely on iOS 13.4.