It's not exposed so you'd probably have to inherit from ShellRenderer and create your own instance of ShellBottomNavViewAppearanceTracker (Android) and ShellTabBarAppearanceTracker (iOS) and access the native controls and modify their height from there. Here's a blogpost from Vladislav Antonyuk showing how to modify it: https://vladislavantonyuk.github.io/articles/Customizing-.NET-MAUI-Shell