IQ test questions are explicitly designed to be things you haven't seen before, solved within minutes per problem. If you've seen them before then the validity of the test is usually invalidated.

Leetcode is effectively the opposite, because each one is usually a CS paper by itself, which by definition took a very hard problem a long time for a very smart person to create and test the solution.

You cannot practically invent the a leetcode solution from whole cloth if you treat it like an IQ test question should be done. It's a sport and you get good at sports via drills until it become muscle memory.