Apple has started distributing watchOS 8.4 globally. The software update arrives for all Apple Watch Series devices from the Watch Series 3 onwards and is roughly a 200 MB download. According to Apple, watchOS 8.4 addresses eight security vulnerabilities and fixes a charging bug that affected some smartwatches.
https://www.notebookcheck.net/Apple-Watch-charging-update-fixed-with-watchOS-8-4-update.596054.0.html