This is what solved it for me

You change the theme in MainActivity, search for line base.SetTheme(Resource.Style.MainTheme)

Remove this line, and the extra bar will go away

The Maui.SplashTheme inherits from Maui.MainTheme.NoActionBar, so by using base.SetTheme(Resource.Style.MainTheme), and not base.SetTheme(Resource.Style.MainTheme_NoActionBar)` you reenables the action bar

see: https://github.com/dotnet/maui/blob/2e4ca4a4d16017fcafbf16d07e6f299456004fff/src/Core/src/Platform/Android/Resources/values/styles.xml#L37