We're running into this too. Unfortunately, .listStyle(.plain) seems to have fallen out of favor at Apple and it took me a while to remember where a plain list might still be in use. I found one, and they've clearly found some workaround: There's a subtle blur and background behind the header view content that you can see is not present on the trailing side ("test 2" is unobscured). I'm not sure how this is being accomplished, whether there's something in private API, or something new in iOS 26 that makes this easy, or whether it's some one-off implementation. But in iOS 26 beta 4, this is not applied automatically behind pinned view content when, in my opinion, it should be. (This should also probably apply to any pinned views in ScrollViews.) With the ability to opt out, of course.

This seems to be fixed in beta 5; the translucent blur effect is now present behind section header views by default with no action needed.