You can use a splash screen and you can call dimensions class with getx while splash screen display. Because size not be null or 0.0 if splash screen display currently. call class after display not before display.

Or you may use didmetrics changed for listen dimensions changing and then refresh layout.

Or you may read my medium story (Fluter UI error after release, release mode render bugs.) you can find my medium profile link on my stackoverflow profile/website section.