I have the same issue. I am a "Routine Guy". Never change, always do the same. Recharge watch before going to bed, sleep in it. Exercise 3-4 times a week. Nothing else, but standard notifications. At night I used to have still 40-50% charge, every day. Now it is hardly enough for a full day. I did not change anything in my routine, nor in the setting of my watch. I have Apple watch Series 9 Stainless Steel. I paid a lot for it. I cannot even use a full day out of it safely now. What's going on Apple?!
The reason why I am with Apple is actually mostly due to my Watch. If you do not fix this, it will be worth for me to change to Tag Heuer watch, with Android phone, Android iPad, windows laptop...etc. And I will be very loud about it for my million followers on Instagram, and Facebook.
No more Apple BS. Fix it, please, ASAP. Totally ruining my user experience, and brand satisfaction.