MacRumors published a story that Apple has released the second betas of iOS 14.4 and iPadOS 14.4 to registered developers.

Apple Seeds Second Betas of iOS 14.4 and iPadOS 14.4 to Developers

Apple today seeded the second betas of upcoming iOS 14.4 and iPadOS 14.4 updates to developers for testing purposes, with the new betas coming a month after Apple released the first betas. iOS 14.4 and iPadOS 14.4 can be downloaded through the Apple Developer Center or over the air after the proper profile has been installed on an iPhone or iPad. Paired with the HomePod 14.4 beta that is only available to a limited number of testers, iOS 14.4 adds new HomePod mini functionality that takes advantage of the mini's U1 chip. There are now visual, audio, and haptic effects when songs are transferred from a HomePod mini to a U1-enabled iPhone 11 or iPhone 12. 

Apple Seeds Second Betas of iOS 14.4 and iPadOS 14.4 to Developers