Header issue when small

[mespeet]

Don't think this really needs an explanation, icon & hamburger menu overlap when window is sized down

[Lewis-Marshall]

This is related to the NavigationView display modes. Examples of the modes can be found here

It's going into the minimal mode when too small for the CompactModeThresholdWidth.

You could try setting CompactModeThresholdWidth="0" in the NavigationView in MainWindow.xaml
This should disable the minimal view.