https://thenextweb.com/microsoft/2020/02/20/microsoft-is-rolling-out-beautiful-new-windows-10-icons/

The first apps to get the new look include Calculator, Groove Music, Mail, Voice Recorder, Alarms & Clock, Movies & TV, and Calendar, according to The Verge, with many more on the way. At least the Mail and Calendar apps should be available to regular Windows 10 users very soon, since they appeared in the Windows 10 Release Preview update track (the others are in the slightly more beta-y Fast Ring).

— Aggiornamenti Lumia (@ALumia_Italia) February 20, 2020