I think it’d be helpful to understand why you want a lightweight distro. I’m running Linux Mint (Cinnamon) on a x201 (~13 years old) and am happy with it’s performance. I doubt you’re going to have any issues with any distro with your laptop (as others have pointed out, mainstream Thinkpads are well supported by Linux).

I know I have friends who run beasts of machines but refuse to “waste” resources on niceties like animations and whatnot. If you’re into that, I assume you want to optimize and tinker, that’s different that lightweight.