I’m seeing the same issue, and it‘s more than just a bit of flickering on some pages.
I consume various digital newspapers that are adding more and more interactive content. Frequently, they have full-screen images in between text. To make them full-size (as opposed to only full-width), they use the viewport height.
Unfortunately, this creates a lot of jank when scrolling even further down - each full-size picture will contribute individually, so two such pictures will cause twice the jank.
Compare the following videos, where the picture of the forest is sized based on the viewport height.
On Safari, scrolling is stable because the image height is stable. The browser‘s UI is on top of the viewport, not around it, so the viewport remains stable.
On Orion, scrolling down shows the UI, making the picture smaller - so the following text actually jumps up, and vice versa for scrolling up. The browser‘s UI is around the viewport, affecting the viewport‘s height as it changes its own.
