This is a good question. However, there is nothing that will tell you this reliably aside from employing the person.

Most people who are smart and get things done will be capable of shipping code, if they can stay motivated. And that’s where having some signal about their interest can help. I want to know if people can inspire their teammates, not just get along, I want to know if they can lead by example, whether they’ll rise quickly, and whether they’ll love it for many years. The essential job functions are just plumbing, the important parts are more than that and aren’t demonstrated by evaluating for narrow, specific job skills.

Look, I don’t in a million years think grinding on Leetcode is some singular answer, or even particularly good. But I don’t see anything wrong with people who are interested doing it, and I also don’t see anything wrong with asking interview questions. I never put a huge weight on such algorithm questions, and there are a dozen other major interview categories. So there’s nothing wrong with asking a few algorithm theory questions, to see the bounds of what people know. I like getting into questions that people don’t know the answer to, whether it opens a conversation about what it means, or whether the candidate has no idea or doesn’t care, that is a small amount of useful signal to me.