However if it refers to an event where if one person did something the past which affects the future then “If John went to school, we’re going to be steamed bread.” would also be correct.

So yes, depending on what you meant to say, both are correct.

But never heard the term steamed bread before.

You always use the past tense with “IF.”

Like, “If i you knew that you wouldn’t ask.”

& “If I were you I wouldn’t argue.”

A lot of people would prefer “goes” in a spoken sentence, but your English teacher will not like seeing that on paper.

Kelby’s “If John went to school, we would be steamed bread.” is the correct sentence

If school has already started but we are not sure if John attended, it could be past (went) because it is something that may already have happened.

if John goes to school, we will be steamed bread.

if John went to school, we would be steamed bread