The Short Version
Apple released watchOS 26.5 RC, fixing two recurring bugs in messaging and workouts on Apple Watch, and added a new Pride Luminance watch face with more customization options.
watchOS 26.5 fixes two bugs that have been annoying Apple Watch users for months: a dual-SIM messaging problem and a Workout app crash. The release candidate also adds a Pride Luminance watch face. Nothing here changes what the watch does, but the messaging and workout fixes are worth installing if either has bitten you.