This is what I found.
Melbourne has overtaken Sydney to become Australia's largest city by population — thanks to a technicality. The borders of the city, which is the capital of the state of Victoria, have been redrawn to include the district of Melton, allowing Melbourne to leapfrog Sydney,
However Sydney Greater Capital city is still around 270,000 larger than Melbourne Greater Capital city.
Capital City Populations, June 2022
Greater Capital City
Significant Urban Area
Sydney
5,297,089
4,892,217
Melbourne
5,031,195
4,929,201