Sure they exist; rare earths exist everywhere; they’re just distributed thinly and so extracting them makes a real mess of the environment.
That’s why nobody wants to mine and refine them in their own country. Destroys the land and generates toxic chemical byproducts. This is what Ukraine would be agreeing to let the US do to it in exchange for… something.
I'm pretty sure this is a scam that Zelenskyy is running on Trump to trick him into making security guarantees and investments into Ukraine, and honestly? Respect the grift.