Try this.
Ok I have had some success in fixing the battery drain on my Ultra 1st gen. iPhone 14 Pro Max (iOS 17.1) & Apple Watch Ultra (watchOS 10.1). Not sure which fixed it or if all played a part but here's what I did;
Unpaired the watch and set it up again restoring from backup, NOT an erase all option, an Unpairing.
Let it restore and chose to setup from backup then restarted the watch and my iPhone.
Removed ALL 3rd party apps from the watch including any watch face apps.
Deleted ALL modular watch faces I had in the watch app on the iPhone. I had one as my current watch face on the apple watch and when I deleted them all from the phone app I noticed it still had the modular face displayed on the watch even after several minutes. Upon looking into the watch faces on the watch itself all my modular faces were still there even though they had been deleted on the iPhone app.
Restarted the watch and iPhone together and once restarted the Modular faces were gone on the watch itself.
I temporarily used a default watch face to verify the battery was draining insanely fast. I used the Toy Story Toy Box one in default settings.
The watch wasn't draining very fast after an hour so I created a couple Modular Ultra faces the Watch App on iPhone and the watch is now draining much more slowly.
I still don't think it's back to where it was but at least it doesn't appear to be losing 90% battery in 6 hours. I hope this helps some people to get their watches working better and not being forced to put it into low power mode as some were suggesting.