Apple updated their compatibility list. The Series 9 is compatible with WatchOS 27 [1]. Still, Series 8 was released in 2022. Less than 4 years old and incompatible? That's quite a departrue from Apple's long-compatibility.
[1]: https://www.macrumors.com/2026/06/08/apple-watch-series-9-mi...
My Series 6 offers me to download the watchOS 27 developer beta, so it seems like someone messed up
They did that before with betas, only to limit the final release.
Did it install?
iPads aren't free from this either but it's a little less severe [2]. For example, iPad Air 4th gen will be the minimum iPad Air and it was released in 2020. The M1 iPad Pro was released in 2021 and will be the minimum there.
[1]: https://www.macrumors.com/2026/06/08/watchos-27-drops-suppor...
j2]: https://www.macrumors.com/2026/06/08/ipados-27-drops-support...