I just updated my Iphone 12 pro max and Gen 6 Apple watch the other day.
My watch was great on battery usage. I could get the battery to last a full 24 hours. After this last update the watch wont even hold a charge for 6 hours.
WHAT DID YOU DO APPLE?????
Try turning Siri off. Does that help? In general though, battery drain can be caused by great many different things.
Have a read in here for some typical reasons:
This appears to have fixed my watch battery drain. Thanks