What is the term for "plain" non-flavored ice cream Me (russian) talked to my partner (american) about ice cream flavors. In Russia and post-USSR plain flavor (creamy-milky one) is extremely popular and often called пломбир. It is the default flavor, in contrast to American default, vanilla.

In the US though, this flavor of ice cream is not a real thing. Is there a term that I can use to find and buy that type of ice cream?

It seems like a common question, and some people call it "cream flavored ice cream", and russian->english translation can be "rich creamy ice-cream".
It's called "sweet cream" ice cream. If you make your own ice cream with something like milk, cream, eggs, and sugar, and you don't put any additional flavoring in it, it's called a "sweet cream base".