Can you please detail me why we cannot use ”the” in the sentence below
Centre appoints Zain as the new Chief Secretary of Panama
why we cannot use ”the ”in this sentence
You can use “the” in the sentence. It would be grammatically correct whether you choose to have “the” in there or not. Even though it is clear there can only be one position as Chief Secretary of Panama, including “the” makes it more prominent.
If you say “the new Chief Secretary”, you are emphasizing the singularity of the role. It does not usually make much of a difference, though, so you could have it either way.