If you are preparing for a technical interview, then LeetCode is like a one-stop solution for you. It is not like other portals which are like a big black box of hundreds or thousands of questions and for solving them you have to pay a hefty amount. It is more like a companion in your journey, a companion which gives you a clear reflection where you actually stand and where you lack. Yes, if you are starting up fresh then it may seem a bit difficult, All you need to do is to be patient and truthful to yourself, do you part honestly, try solving every question and its completely ok to seek help for hard ones and then they provide you Discuss section via which you can see and analyze codes of great Coders.
It also offers other sections for practice such as Database, Operating System, System Design etc which are also very important and often neglected while preparation.
So Leetcode is all you need for your interview preparation.