Apple has started a new developer beta cycle for iOS 14.4, iPadOS 14.4, tvOS 14.4, and watchOS 7.2 which likely contain bug fixes for the recent public release.
The latest builds of each operating system can be acquired from the Apple Developer Center for devices enrolled within the testing program, as well as via an over-the-air update on hardware already using beta software. A public beta build usually arrives some time after the developer counterparts, as part of the Apple Beta Software Program.
The first developer beta of iOS 14.4, iPadOS 14.4, tvOS 14.4, and watchOS 7.3 doesn't have any notes on new features or improvements. Features will likely be discovered as developers begin to crawl through the released software.
This beta cycle comes after Apple released its latest software updates to the public. Both iOS 14.3 and iPadOS 14.3 added support for Apple ProRAW, Apple Fitness+, and AirPods Max. The watchOS 7.2 release brought improved ECG functionality and VO2 Max measurements. The tvOS 14.3 update included Apple Fitness+ and improved Apple TV+ content discovery.
AppleInsider, and Apple itself, strongly suggest users avoid installing betas on to "mission-critical" or primary devices, due to the potential for data loss or other issues. It is instead recommended to install betas onto secondary or non-essential devices, and to ensure there are sufficient backups of important data beforehand.
Update, Dec. 17, 2020: Apple has released public beta versions of iOS 14.4 and iPadOS 14.4.