Apple releases updates for watchOS 5 and watchOS 8 in order to keep core functions alive.

Juli Clover from MacRumors:

watchOS 5.3.10 is available for the Apple Watch Series 1, Series 2, Series 3, and Series 4, while watchOS 8.8.2 is available for the Apple Watch Series 3, Series 4, Series 5, Series 6, Series 7, and original Apple Watch SE.

According to Apple's release notes, the updates extend the certificate that features like device activation, iMessage, and FaceTime need to function. The certificate update ensures that these apps and features will continue to work after January 2027, which is when the existing certificate was set to expire.

watchOS 8 is the final version of watchOS that's supported on the Apple Watch Series 3.

watchOS 5 is the final version of watchOS able to be installed on an Apple Watch Series 1 or Series 2 using an iPhone 5s, iPhone 6, or iPhone 6 Plus. The Series 1 and Series 2 do support watchOS 6, but installing watchOS 6 requires an iPhone 6s or later.

To add to Juli’s bit:

• Series 4, Series 5, and the original Apple Watch SE can be updated to watchOS 10, but watchOS 10 requires an iPhone XR, XS, or later, and relearning the controls.

• Series 6 and Series 7 can be updated to watchOS 26, but watchOS 26 requires an iPhone 11 or later, or iPhone SE 2nd generation or later.