The Qt Quick application wizards generate projects with a qtquickcontrols2.conf that looks like this:

[Controls]
Style=Default

The result is a build error:

:-1: error: C:\Users\alportal\AppData\Local\Android\Sdk\ndk\21.3.6528147\toolchains\llvm\prebuilt\windows-x86_64\bin\x86_64-linux-android-strip:C:\Users\alportal\Documents\build-Android-debug-test-qmake-Android_Qt_6_0_0_Clang_x86_64-Debug\android-build\build\intermediates\stripped_native_libs\debug\out\lib\x86_64\libqml_QtQuick_Controls_Universal_impl_qtquickcontrols2universalstyleimplplugin_x86_64.so: No such file or directory

Which in essence says that there is no "Default" Style plugin for Android Qt 6. A plugin for "Material" is there for Qt 5 and Qt 6.