air travel – Can one cancel the return flight with Qatar Airways and if so, what is the fee?

https://www.qatarairways.com/en/travel-with-confidence.html (mirror) states:

(Applicable for tickets issued up to 30 April 2021.) You also have the option to refund the unutilised value of your ticket to the original form of payment with no penalties or refund fees.

Assume a passenger purchase a round-trip ticket with Qatar Airways before 30 April 2021. Can the passenger cancel the return flight with Qatar Airways and if so, what is the fee if any?

I’m interested to know when the return flight is canceled before the passenger took the departure flight, as well as when the return flight is canceled after.