Is this true... seller needs to request the buyer to cancel when it's the buyer and not the seller who wants to cancel?

The seller has to initiate it.  The seller has to send mutual cancellation request and the buyer has to respond to it.

As said above; you have to choose if you want to send the cancellation request or after 4 days open not payment case.  Or if you just leave it and do nothing, but that means you will pay the FVF on the item, and if you re-list and sell the item the buyer can come few weeks later, pay and then expect the item, and can leave you FB for 60 days.