Just talk to the person, ask them about projects they’ve worked on, problems they’ve solved etc. you’ll learn far more about them that way than getting them to put on a dog and pony show at a whiteboard!
Why not both?
I think an extra hour to talk will give me more information than watching them balance a binary tree.
For many people the stress of the leetcode session is just awful, I don’t think it’s a nice thing to inflict on someone if you’re ultimately going to disregard the outcome anyway!