Was. The indefinite pronouns: anyone, everyone/everybody, someone/somebody, no one/nobody are always singular, so singular verbs are used. However, there are some indefinite pronouns (e.g. some, all) can be plural, depending on what they're referring to.

You would use the verb "was" not "were" particularly because words like "everyone" and "everybody" are treated as singular not plural. I'm not sure why, but I think it has something to do with the ending words of those words. For instance, in the word "everybody", -body is singular. You can also think of it as not using the verb "are" (present simple) for everybody, everyone, anyone, no one, etc., so you would not use "were" for those words either.

Was is singular and were is plural. Both are past tense. For example, John WAS here yesterday. John and Joe WERE here yesterday. Hope this helps

was

I mean - everybody was or everybody were? No one was or no one were? Anyone was or anyone were?