MacRumors published a story that Apple has released the third beta of iOS 15.4 and iPadOS 15.4 to registered developers.
Apple Seeds Third Betas of iOS 15.4 and iPadOS 15.4 to Developers
Apple today seeded the third betas of upcoming iOS 15.4 and iPadOS 15.4 updates to developers for testing purposes, with the new software coming one week after Apple seeded the second betas of iOS 15.4 and iPadOS 15.4.
Apple Seeds Third Betas of iOS 15.4 and iPadOS 15.4 to Developers
Developers can download iOS 15.4 and iPadOS 15.4 through the Apple Developer Center or over the air after the proper profile has been installed on an iPhone or iPad.