It's basically screen tearing, apparently because the top and bottom of the display (or left and right in other orientations) refresh at different rates. iFixit suggests its a controller issue.
> Update, 9/28/2021: In response to our inquiry, Apple has told us that the "jelly scroll" issue on the 6th-generation iPad mini is normal behavior for LCD screens.
> Update, 9/30/2021: An iFixit teardown suggests that the iPad mini's more noticeable scrolling issue is a byproduct of how the display controller is mounted.
I'm guessing Apple is using an IPS panel meant for landscape orientation (i.e. the image scans from the top/bottom) in a device mostly used in portrait orientation. This causes rolling shutter distortion when scrolling contents.
It's basically screen tearing, apparently because the top and bottom of the display (or left and right in other orientations) refresh at different rates. iFixit suggests its a controller issue.
> Update, 9/28/2021: In response to our inquiry, Apple has told us that the "jelly scroll" issue on the 6th-generation iPad mini is normal behavior for LCD screens.
> Update, 9/30/2021: An iFixit teardown suggests that the iPad mini's more noticeable scrolling issue is a byproduct of how the display controller is mounted.
https://arstechnica.com/gadgets/2021/09/2021-ipad-mini-suffe...
FWIW, my 5th Gen Mini doesn't have this issue.
I'm guessing Apple is using an IPS panel meant for landscape orientation (i.e. the image scans from the top/bottom) in a device mostly used in portrait orientation. This causes rolling shutter distortion when scrolling contents.
They are referring to the screen lagging/tearing while scrolling