With iCloud, you can sync the Reminders app so that you are alerted to reminders from all of your devices. If you don't want or need reminders duplicated across your Apple ecosystem. Thankfully, it's easy to turn off these duplicate reminders.
On a Mac, open System Preferences and select iCloud. From the list, uncheck the box for Reminders.
Similarly, on an iOS device, go to Settings > iCloud. Then tap the toggle switch to off for Reminders.
