How do I disable Cortana?
Settings->Cortana & Search Settings
You can't absolutely, positively disable Cortana because there is a process named Cortana that is part of the OS and integral to doing Windows Search. You can, though, disable Cortana as an electronic personal assistant (and/or remove anything she already knows about you in the cloud) and having her include web results as part of her searches (which uses Bing to get them).
I am still awaiting clarification from Microsoft as to whether they recognize a difference between the Cortana process, which one really can't get rid of, and the Cortana Service [which is what I think of as "full Cortana personal electronic assistant" functions]. One should be able to avoid using the Cortana Service if one so chooses, but it doesn't look like the Cortana process is optional in any way.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1809, Build 17763
Travel is fatal to prejudice, bigotry, and narrow-mindedness, and many of our people need it sorely on these accounts. Broad, wholesome, charitable views of men and things cannot be acquired by vegetating in one little corner of the earth all one's lifetime.
~ Mark Twain