Cortana on Android and iOS is no more; Microsoft recommends using its To Do app instead
Cortana remains deeply integrated within Windows 10, for better or worse. Microsoft launched Cortana as a virtual assistant to challenge Apple and Google's alternatives, but it has since repositioned its offering as a 'productivity assistant', instead. It remains to be seen how productive Cortana will be going forwards though, as Microsoft has now stopped supporting its assistant on Android and iOS.
Microsoft has been rather vague in its support document, but ceasing support means that it has pulled the Cortana app from the Apple App and Google Play stores. Existing installations will continue to work though, as will new installations if you download the APK via a third-party website. Incidentally, it last updated its Cortana Android app in February 2021.
Reminders and lists will no longer function in the deprecated Cortana mobile apps, either. If you wish to access these, then you can do so in the Microsoft To Do app, which automatically syncs any tasks that you have set up in the Cortana app. Alternatively, you can view your reminders and lists on the Cortana app on Windows 10.
Overall, Microsoft's announcement is a sad end for Cortana, which was at the heart of Windows Phone 8.1 and Windows 10 Mobile. Cortana will probably continue to live on in Windows 10 for a while, but we would not be surprised if Microsoft phased out its productivity assistant altogether at some point.