As previously announced, Microsoft will shut down the Cortana app for iOS and Android today. Cortana is the company’s virtual assistant, rivalling Siri and Alexa.
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.
After March 31, 2021, the Cortana mobile app on your phone will no longer be supported. 
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