Xenon is very rare too and currently without substitute for certain medical applications, but more interestingly it produces psychoactive effects that could shed light on stuff no other substance apparently can: https://pmc.ncbi.nlm.nih.gov/articles/PMC11203236/
There's two trillion kilograms of it in the atmosphere. People sometimes get confused because it's one of the rarest element in the Earth's crust. But that's because it floats away.
