https://wccftech.com/apple-stopped-signing-ios-14-3-downgrade-no-longer-possible-heres-what-you-should-know/

Apple saw fit to release iOS 14.4 last week with a boatload of bug fixes and performance enhancements. Other than this, the build also featured a handful of forward-facing additions. While iOS 14.4 is all out and about, following its usual time frame, Apple has now stopped signing iOS 14.3. What this means is that it is no longer possible to downgrade to iOS 14.3 from iOS 14.4. If you were having concerns regarding iOS 14.4, the window to downgrade to iOS 14.3 is now closed. Scroll down for more details on the subject.

Before today, you had the option available to downgrade to iOS 14.3 from iOS 14.4. Now, Apple has stopped signing iOS 14.3 that takes away any liberty to download and install the previous build. Generally, when Apple stops signing a specific iOS build, it is no concern to the average user. However, users who are more inclined towards experimentation and jailbreak would have to keep a check on such stuff.