I have the same problem, S21 Ultra Exynos, battery drains at a terribly fast rate. Actually, the entire UI seems broken the notification scale and font, why Samsung releases an update without testing for negative impact on user experience with their devices. Disappointed.
My S21 Ultra's battery is definitely draining faster now I have Android 12 compared to when I had Android 11. Hopefully it will get better as we receive future updates.