That's weird, I started to see the Sleep Score on my iPhone on iOS 26 two days ago with the GM release. My AW Series 9 was still on watchOS 11.6 and not on any betas. I finally updated to watchOS 26 last night. While I was on 11.6 I didn't see any sleep data other than the already present graph. After the update it's nice to see a separate Sleep Score which after three days worth of data I can feel pretty good about. I look at the graph daily so I can see how they're calculating it.
Also, the Series 9 might be the best value Apple product in years. The chip hasn't changed since it was released, and it keeps getting new software features like Sleep Apnea detection (which I need) and hypertension detection, though the latter may only show up if for some reason I get off my beta blocker. I'm old.