People joke about "my grandfather opens his browser and types 'Yahoo' into Bing, clicks the link and types 'Google' in to Yahoo, clicks the link and types 'Facebook' into Google to get to Facebook", but it's not that wild an exaggeration of how much of the developed world -- which is not computer-literate -- uses the web. That's part of why walled gardens and native-feeling app experiences are so successful.
Isn't there a service which shows popularity of search terms? That would be one way to get a handle on frequency.
Found it:
https://www.google.com/trends/explore?q=Facebook
I don't know this tool well enough to know if this is for queries where the only term is Facebook. Happy to be corrected!
"Navigational searches" are a thing and they are very optimized by Google. But yes, auto-complete likey handles a lot as well.