Hi Максим how are you? The phrase that is typically said, is "I second that" (to be in agreement with). It would probably be toward the more casual (informal) side I would say. Good question, let me know if that makes sense!

I'm next to him is the right term

Yes you are right this sentence is used for telling someone that you agree with what they are saying . " i second that " we can say that an idiomatic way of saying you agree with someone's opinion and support them .

Right means correct

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