'Everyone' is treated as singular (aside from 'everyone are' sounding completely wrong).
I think that's the case for all the "every <noun>". "Every human is a person", for example. This would make sense, to put it in programming terms - the verb applies to an element in an array of people, not the array itself (which would be plural): for every single human, that human is a person.
Drop the "every" part and you can see the word that needs to be agreed with.
This also applies with "some" https://en.wikipedia.org/wiki/Quantifier_(linguistics)Part of the confusion may be that "everyone" is a single word while the example sentence in the Wikipedia article has a non-compound example.
The quantifier does not change the grammatical number of the subject.