LeetCode has weekly contests that have problems that might be too easy for the top contestants in here, but are nevertheless interesting, you can win a T-shirt each time, and are a good interview prep. Sadly, they are always the same time which is not friendly for Europeans (Sunday 3:30 AM CET).

Now admins have said that if they get enough requests for European timings, they will add it. If you have a LC account you can write in this forum post: https://leetcode.com/discuss/general-discussion/234262/Coding-contests-are-starting-way-to-late-for-Europeans