Waited so patiently for our report but we have not submitted it yet which underlined word functions as a coordinating conjunction in the sentence

"But" is one of the coordinating conjuctions (For, And, Nor, But, Or, Yet, So) and indicates a contrast between two independent clauses.

Example:

"Waited so patiently for our report BUT we have not submitted it yet"

IMPORTANT:

An independent clause is one in which a complement is not necessary to make sense. If you take the sentences before and after the conjunctions, they make sense by themselves; there is no need of complement:

- Waited so patiently for our report  

- We have not submitted it yet.