https://www.pcgamer.com/how-to-disable-cortana/

Cortana is the digital voice assistant built into Windows 10 that was designed to make interacting with the operating system simple and intuitive. Like Siri for Apple, Alexa for Amazon and Google’s unnamed voice assistant, Cortana has been configured to help you perform basic functions with just your voice. But if you're not interested in those voice assistant features and don't want Cortana piping up when you click on the search bar, or you're worried about your privacy, here's how to shut it off. Microsoft doesn't make it easy, but we'll walk you through the process. 

When Windows 10 was first released it was simple to switch off Cortana, but doing so broke Windows Search. Turning it off now doesn’t break search in quite the same way, but it can have an impact. It's also not quite as easy as it used to be. Changes were made in the Windows 10 Anniversary Update to how Cortana integrates into Windows and how we can turn it off. Not all previous methods work, but the steps in this guide will.