I don't know when did this start but QR now started to label their seats as Extra Legroom, Preferred, and Standard as November 2020.
When choosing seats on the QR website;

Extra Legroom seats are marked with Blue
Preferred seats are marked with Orange
Standard seats are marked with Burgundy.

I personally am a QRPC Platinum member so seat selection is free of charge so I can't tell anything about the pricing of the seats for non-status passengers, elites of other oneworld partners, QRPC Silver & Gold members.

For your info, the Preferred seats do not have extra legroom but have a favorable location in front of the cabin.

Although here are examples of how seat maps look;
Note: There are some glitches such as alignment of the seat maps but I am sharing these as an idea for you to understand how it looks like

Airbus A320 ( C12Y120 configuration )
Rows 8, 11, 12 -> Extra Legroom
Rows 9, 10, 13 -> Preferred
Rows 14 and below -> Standard


Airbus A350-900
Rows 16, 30 & Seats 17C/H -> Extra Legroom
Rows 17 to 21 ( excluding seats 17C/H ) -> Preferred
Rows 22 to 29 & 31 and below -> Standard