After I updated my Series 8 to watchOS 10.1 I had terrible battery drain. Something like losing 10% in 20 minutes.
I tried to force a restart (if you’ve never done hold the Digital Crown and the side button together until the Apple Logo pops up).
After that things got back to normal. Lost about 11% with an hour of GPS workout, which would equate to a bit more than the 7 hours of GPS workouts that Apple states (and I’m on 98% battery health).
I had the same issue and also had problems with apps working on the watch like YouTube Music (wouldn’t sync or just have an error message). Tried all kinds is settings changes, repaired multiple times, both from a saved back up and as a new watch setup. No luck and battery continued to drain at a rapid rate. Finally did the suggestion of removing the Moby app on the phone and boom. No longer have any issues. How does one app cause so much trouble?! Thanks to those who suggested that.