Here’s an interesting map of what’s considered the first day of the week in different countries. FWIW I wasn’t sure what it’d say for Australia – in unofficial use I’ve seen both, like calendars usually start with Sunday while weekly planners usually start with Monday. My own personal instinct has the week starting on Monday, so that’s how I set up all my devices, but my partner feels like it starts on Sunday (and likes to tease me some Saturdays by going, “next week…” when what he really means is, “tomorrow…”).