Yesterday I tested my S21 Ultra ( exynos UK ) with a Bixby routine I use/used on my S20 Ultra. The routine is having M/S drop to 60hz in specific apps where there is no real benefit of 120hz. For me, apps like YouTube, Amazon Shopping, ebay, messaging apps etc, leaving social media apps, browser etc at 120hz. Below is my screen on time in between yesterday's and today's full charge, mostly using Facebook and YouTube, Facebook being 120hz too, and leaving 10% battery. I use FHD+ resolution with Dark Mode, no gaming, I have 19 apps in total added to the routine. I understand this is basically what Adaptive M/S is for, but this routine has given around 1 hour 30 minutes additional SoT than when using Adaptive 120hz full time, give or take 15-20 minutes for different usage patterns. This could be useful to heavy users.
Edit: if applying this routine, use the same res for both 120hz and 60hz, having the res change makes "some" apps flicker when opening. Just thought I should add that to the post.