This is covered in the "The PC Is Not a Typewriter"[1], by Robin Williams. (No, not that Robin Williams.) I adjusted from two spaces to one back in 1999 or so, when I read this book, and the adjustment wasn't as painful as I thought it'd be. I learned on a typewriter in the late '80s.

For some reason, Stephen King uses two spaces between each word in his Tweets.[2] Not sure if this is some statement he's making or a technical glitch.

[1] https://www.amazon.com/PC-Not-Typewriter-Creating-Profession...

[2] https://twitter.com/StephenKing/status/1678579628686946304?s...

The book “the Mac is not a typewriter” (https://www.amazon.com/Mac-Not-Typewriter-2nd/dp/0201782634) may help get them some idea about style. It is 15 years old, targets print, and is aimed at Mac users, but that doesn’t matter that much.

(For PC users, there is “the PC is not a typewriter” (https://www.amazon.com/Pc-not-typewriter-Robin-Williams/dp/0...), but that is even older, so I’m not sure it will be more useful than the original, unless your users are using WordPerfect or Ventura Publisher)

Robin Williams devotes a chapter of her book, "The PC is not a Typewriter", on the subject. She concurs.

http://www.amazon.com/Pc-Not-Typewriter-Robin-Williams/dp/09...