A post above (can't see it just now) asks how we would go about 'defining the harmony of a chord without a 3rd note’, but you have to be careful with citing needing to use at least 3 notes to define the 'harmony' of a chord, with harmony itself defined as 'any simultaneous combination of tones.'
Playing two notes together creates a harmony, whether that harmony then falls into the western music definition of a chord is another question.
Some may say it's semantics, or pedantry. I prefer to think of it as academic
Si