Update: AppleInsider and MacRumors both now report that these updates were not meant for the public but were briefly, and inadvertently, published to the main release channel. Apple subsequently pulled the initial downloads and has re-released them as downloads exclusive to developers.
iOS
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UPDATE: American Printing House for the Blind (APH) has issued a warning that there are connection issues for the Mantis and Chameleon braille displays after upgrading to iOS 14.4; and recommend that you turn off automatic updates and do not upgrade until a resolution has been found: