Today it seems to be a domestic Sydney Melbourne flight (Flightradar24) but back then must have been an international flight.
If by "today" you mean a year ago, on 19 Jan 2022 QF40 was APW-SYD-MEL on that day only. That was the only QF40 for 2022. It would have been a flight facilitating Seasonal workers from the Pacific Islands during COVID. It did a few similar to SYD and BNE in 2021. That's all Flightradar has got.
Do you still have your old Passports? Maybe you can marry up the arriving countries stamp to get your outbound legs?
If you have the flight numbers and dates, see if the relevant Airline's
PR department will help you? A couple of emails might get you your answers.