Anecdotally I would say that oat based milk is taking over the world (probably because it is sweeter). But it feels to me like Veganism and Vegetarianism are still quite niche.
I also learned that while they almost always say they're unsweetened, that's kinda... not wrong, but misleading, as most oat milks use a production process that creates sugar.
There are no-sugar or almost-no-sugar oat milks that don't do this, but they're rare.