FWIW, I have just tried to reproduce this jelly effect on my iPhone 12 mini scrolling at different speeds in both vertical and horizontal iPhone orientation - no issues at all. 🖐
I can see it on my 12 mini when horizontal and scrolling up and down. It's absolutely there. 60Hz screens take 16ms to refresh top to bottom. They are always drawing new lines and never refresh everything at once, it's just the nature of displays.

Understanding Display Scan-Out Lag With High Speed Video - Blur Busters
High Speed Video Makes Display Refresh Behaviour Easy To Understand Blur Busters released the high speed video of motion blur reduction in year 2012, and we were the world's first website to measure the input lag of G-SYNC via high speed camera in 2014. New TestUFO Test For High Speed Cameras We...
