Translated by google:
>>Hello Apple community.
I used to have a 40mm Apple Watch SE 2 that I loved, but the battery life frustrated me—even though I managed to get 44 consecutive hours of use without charging (in Low Power Mode).
A week ago, I switched to a 46mm Apple Watch Series 11, and the battery life has increased to 72 hours, still in Low Power Mode.
My question is: is it worth keeping the watch in Sleep Mode indefinitely to extend the battery life even further? Has anyone tried this, and how many extra hours can you gain this way?
Thanks for your answers.<<
Apple tested the battery life for the Apple Watch 11 and stated in this article, that Low Power Mode will get you at up to 38hours of All-Day Battery Life, or 24hours in normal mode.
Apple Watch - Battery - Apple
But the downside to using Low Power Mode is, that you will lose main features of the watch:
...
Low Power Mode turns off these features
- Background blood oxygen measurements, including during sleep
- Background heart rate measurements, including during sleep
- Collection of heart data for hypertension notifications
- Heart rate notifications for irregular rhythm, high heart rate, and low heart rate
- Always On display
- Gestures (double tap and wrist flick)
- Start workout reminder
- Time in Daylight
...

...
copied from: Use Low Power Mode on your Apple Watch - Apple Support
Utiliser le mode économie d’énergie sur votre Apple Watch - Assistance Apple (FR)
Did you know that there is also a French speaking Apple Community?
You might get more answers in these forums from native speakers.
Communauté d’assistance Apple officielle
Since the Apple Watch Series 11 charges much faster than your old watch, if using the 20W Apple power adapter, I would not enable Low Power mode during the daily use.
You can recharge your watch in a couple of minutes, and the use of the Optimised Charging feature is also recommended by Apple.
About Optimized Battery Charging on Apple Watch - Apple Support
À propos de l’optimisation de la charge de la batterie sur l’Apple Watch - Assistance Apple (FR)
I do not use the Low Power Mode on my Ultra 2, I would lose too many features, especially for the daily fitness workouts and monitoring sleep during the night.