You can visit luogu and many hard problems in Chinese are on here. The site has tons of problems from Chinese contests, and sometimes you’ll even find some technique there.

I recommend using UOJ, which contains many challenging problems of generally high quality. The only drawback is that most problem statements are only available in Chinese. You might consider using AI to translate the problem statements.

Also LOJ.

As a Chinese CPer, I don't know how the guys in high school become LGM. Thus, I believe there would be a secret website they don't want to let us know.

Or their coaches all have superpower and they can invent super ultra awesome problems...

I'm not a high school student anymore so I can't get the secert key either

Им там 100% какую то инъекцию вводят , и на завтра уже могут шпарить 3500

become a femboy

First, try this