Those are settler colonies, a completely different kettle of fish. From the point of view of the (majority) settler population, they gradually ceased to consider themselves as British and underwent a multi-step disentanglement of legal and constitutional connections to the UK beginning almost a century ago but still ongoing. From the point of the (minority) indigenous populations, well I'm sure it varies but they may not agree that a withdrawal has occurred...
It still strikes me as a bit weird that Canada did not have its own constitution, as in technically completely independent of the British Parliament, until 1982.
And technically the head of state is…well it’s complicated.
Yeah, similar stories and timeline in other former dominions. I find https://en.wikipedia.org/wiki/Sue_v_Hill fascinating, when a court in Australia was forced to consider whether the UK was a foreign power.