Nutritional yeast is great on popcorn! It was one of my first "vegan" buys. It took me a while to like it on other things, but I liked it popcorn right away! So do my kids. You can buy in it in a natural or health food store,mine is in refrigerated containers sold by weight. Lots of B vitamins, Red Star most popular brand.
If you're making air popped you should try an olive oil mister.
Don't let the perfect be the enemy of the good