The universal nature of mathematical truth isn’t dependent on agreement. Instead it’s only universally true when you include all those seemingly unspoken “agreements.”

> isn’t dependent on agreement

It is by definition. If you disagree, go write a mathematical proof that 1 = 1. There are many in the world who would love to see it.

Hardly, there are sets of axioms where 1 = 1 which already show this in exquisite detail.

I'm not sure what you mean by this, particularly this phrasing: "sets of axioms where 1 = 1". 1 = 1 is an axiom, not something that's proven by any set of axioms.

But I'm willing to believe I'm simply naive here. You say there is some set of axioms which prove that 1 = 1. Are those axioms not agreements? Since you seem to be familiar, what are those axioms?

What you are missing is 1 = 1 isn’t inherently true on it’s own.

There are sets of axioms where 1 = 1 is false, different sets where it’s undefined, and finally sets of axioms where 1 = 1 is true.

However, for a given set of axioms there is no choice and nothing to agree upon. That’s what makes math universally true.