Title not showing on any application

Hello,

I can not display the title in the action bar. I have Android 7.1 and no sample displays the title. My tablet use Android 7.1. I have this problem on any sample downloaded on the Website Xamarin. Is it a Xamarin bug or Is there a setting to make in a visual studio or on a tablet. The title is displayed on Xamarin Live Player but not on the tablet. Do you have an idea ?
Best Regards,
Kévin