I am facing the same problem. In my case we have a tab bar at the bottom and content is partially covered by the tab bar. Our web frontend team has already been working on adding "viewport-fit='cover'" setting and using "env(safe-area-*)" values for the body paddings. This way we can at least "fix" our web content when displayed in our app. What I couldn't figure out so far is why Safari on iOS 26 doesn't seem to have an issue with all of that. Content is just magically correctly positioned all the time. What is the the iOS 26 Safari app doing that we don't/can't do? So far I haven't seen any fix regarding this up to current 26.2 developer beta.

Thanks for your response! If iPhone with paired Apple Watch doesn't return true when running canEvaluatePolicy(.deviceOwnerAuthenticationWithCompanion, error: &error), in which case would this return true? (tried to post this as comment to your answer, but always got an error doing so)