Apple has begun to distribute watchOS 8.4.1 to certain Apple Watch users following the release of watchOS 8.4.1. That’s because only Apple Watch Series 4 and later models appear to get the update.
Apple Watch Series 4 and later devices gets the watchOS 8.4.1 update
No specific changes were mentioned in the update’s release notes, but they do say that watchOS 8.4.1 is intended to fix bugs that only affect Apple Watch Series 4 and later devices. Although the Apple Watch Series 3 can also run watchOS 8, it does not appear that today’s upgrade has been delivered for it.

watchOS 8.4.1 is released in order to fix some issues and bugs of the Apple Watch Series 4 and later. Visit the official website for more information.
A bug in watchOS 8.4 that prevented Apple Watch from being recharged with some third-party chargers has been fixed, according to the release notes. Although there are no major changes in watchOS 8.5 beta or iOS 15.4 beta.