This will also remove the search box from your taskbar.

To hide Cortana in Windows 10, November 2019 Update and earlier versions: On the taskbar, select Cortana, hover over Cortana on the menu, and then select Hidden from the side menu. Then select the Clear button under Chat history. You can clear your chat history with Cortana on a device by signing out or by going to Cortana > Settings > Privacy. You can learn more in the Microsoft Privacy Statement. In the May 2020 Update and later versions, you must be signed in to use Cortana. When you’re signed in, Cortana learns from certain data about you, such as your searches, calendar, contacts, and location. To hide Cortana in Windows 10, May 2020 Update and later versions, select the Cortana icon in the taskbar and uncheck Show Cortana button. You can also manage your privacy settings following the steps below. If you don’t want the digital assistant to be visible to you, you can hide Cortana from the taskbar. Cortana is part of Windows 10 in the locales where Cortana is available.

Reinstall cortana app