Everyone and every one are easily confused words.
The spell-check application of most word processing software programs would not catch a slip-up of these two words. Spell-check is looking for words that aren’t in its dictionary, and words that resemble words in its dictionary but are possibly spelled wrong. Spell-check isn’t perfect. It doesn’t know and can’t guess what word you wanted or what word you meant, it can only judge the words on the page. If you used words that are all spelled correctly, it gives you a pass anyway.
Autocorrect suggests words that start with the same letters. It suggests what word you may want to save time, but quite often, its suggestions couldn’t be more off base and produces humorous results.
Every one is a pronoun. It describes a group of people, but on an individual, person by person basis.
Everyone is a pronoun. It is used to describe a group of people in a very general way. A similar term, everybody, is also a way of talking about a group of people, but it comes across as a bit more casual.
The following story uses both words correctly:
Everett wasn’t convinced by Evaline that everyone thought he wasn’t cut out to be class president, so he went around and asked every one of his classmates what they thought. He changed a lot of perceptions and ended up winning.