Hi @A5adm I take it you are using a lot of optimsation techniques, are you using a power saving mode and do you use 5G much? Dark modes at times of the day an option but not a fan of this being on constantly, personally want balance of best experience and battery life. Some ideas in this article, though you may have tried many of them. https://www.sammobile.com/news/7-tips-improve-galaxy-s21-ultra-battery-life/
Have you wiped the cache partition lately as that can help, if nothing else makes much difference could try a factory reset (after backing up of course) The battery life on my S21 Ultra after the initial period has been fairly impressive generally.
I do not work for Samsung or make Samsung Products but provide independent advice and valuable contributions.
My Device- S21 Ultra 5G ( SM-998B/DS ) CSC= BTU , 12GB/256GB
One Ui 4.0,Android 12 Official Version.
@A5adm ,Hello, could you also include these two important settings: In Device care, three points up right / Action Automatic and active: Automatic daily optimization and Adaptive energy saving, greetings.