I might add that if you don't use Google search bars (I figure I can use a browser for search, why would I want widget cluttering my desktop) or voice search in Maps you can disable Assistant as well as turning it off by disabling the Google app. The reason I did this was that if my finger lingered on the wrong button for too long I would get a prompt to turn Assistant on, and disabling that app was the way to get rid of those prompts.
(Now if only there was a way of getting rid of those dishonest pop-ups asking me to "turn on device location" that some apps produce - dishonest because I do have location on, what that prompt does is turn on the wireless network part of the location service, which allows Google to collect more information. But if you click OK it just does this silently, and doesn't show the privacy notice that you see if you turn "Google location accuracy" on via the Settings. In my book that is doubly dishonest.)