My Apple watch (Gen. 4) says OS 7.6 is the latest available. Do I have to believe that?
Scroll down in the update pane and you should find the watchOS 8 install option.
I had the same problem. I finally checked profiles on the Apple Watch and saw a profile for the watchOS 7 beta program. This prevented my watch from upgrading to watchOS 8. I removed the profile and then I was able to install the new version.
My Gen. 6 watch said “Unable to download…” but when I checked the Watch app on my iPhone it said I had to update the iPhone OS before I could install the Watch OS. So, that could also be your problem.
Yeah - that was it!