The definition of a mole provided in this article is no doubt correct, but it’s not how it was taught in my high school chemistry class.

For others with the same nagging thought, the explanations of Avagadro’s Law feel more familiar: https://www.britannica.com/science/Avogadros-law

In particular:

The specific number of molecules in one gram-mole of a substance, defined as the molecular weight in grams, is 6.022140857 × 10^23, a quantity called Avogadro’s number, or the Avogadro constant. For example, the molecular weight of oxygen is 32.00, so that one gram-mole of oxygen has a mass of 32.00 grams and contains 6.022140857 × 10^23 molecules.