As of March 31, 2021, Microsoft’s Cortana app on iOS and Android will no longer be supported.
As of March 31, 2021, the Cortana content you created–such as reminders and lists–will no longer function in the Cortana mobile app, but can still be accessed through Cortana in Windows. Also, Cortana reminders, lists, and tasks are automatically synced to the Microsoft To Do app, which you can download to your phone for free.
Check It Out: Microsoft Shuts Down its Cortana App on Mobile