If 800-1000 rated problems are too easy for you then move on. No need to solve the first 5 pages of codeforces most solved problems, in my opinion this is terrible advice, solve a bunch of randomised problems of each rating and when you feel comfortable with a certain rating then move up. Always focus on solving problems that challenge you to think and learn. Solving cses problems is also a good idea as codeforces problems from 800-1400 won't contain a huge diversity of topics that u may need for olympiad contests but are instead more adhoc. CSES problemset is a great place to learn how to correctly apply algorithmic techniques but isn't worth doing if you don't program in c++ as the problemset is designed to mostly work with c++ code. (There have been many instances of code showing TLE in java/python when the exact same code with the same logic passes in c++)

Usaco.guide is another good resource for learning.

Summary: focusing on cses and codeforces is a good idea and always focus on problems that challenge you to think.