please note that using the navigationBarTranslucency property causes the Page to fill the whole screen (because the navigation bar blends through), so your page layout must handle the top offset.
Your error indicates that you are using wrong anchoring within a layout component. For example, you cannot use horizontal anchoring within a Row, because the Row tries to handle the horizontal layout. You can still use vertical anchoring (e.g. anchors.verticalCenter, or anchors.top) but not horizontal (e.g. anchors.left). Using such wrong anchoring breaks the layout (error message: “Row will not function.”)
For pages that step away from the default look, developers will need a custom implementation in any case. Same goes for other Theme properties that affect the NavigationBar. This would require some bigger changes in the SDK. Due to the current setup of how Theming and the NavigationStack / Page implementation work, we do not have planned to add a property for this at the moment.