Existing issue?

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What happened?

See also: flutter/flutter#120937

If openInSecondScreen is true, we unconditionally use a TwoPaneScreen. This is implemented as a OverlayRoute, which is typically used for popups and modal menus, so it does not hide the contents of the previous route. This leads to dramatically reduced rendering performance and no page transition, even if on a non-foldable device.

Instead the hinge check should be hoisted into route selection so that we always use a MaterialPageRoute on non-foldable devices

https://github.com/flutter/gallery/blob/main/lib/routes.dart#L133

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