Which other OJs are good for olympiad preparation

should I practise only usaco or should I practise on OJs if so which oj should I use? (olympiad is my first priority )

I mean, they both have programming problems, and you can submit problems on most OJs and the official USACO website. I’m not sure what you’re asking for here.

people say that codeforces is not good for informatics olympiad preparation . I am asking which other ojs have siimilar problems that show up in national olympiads

https://usaco.guide/general/oly might be helpful?

where did you hear that cf is not good for olympiad prep?

people say that codeforces problems are different in type compared to OI probs

yea ig I can see that to some degree. Though speaking from personal experience, cf is pretty helpful for building observational skills.