'How to set Flutter DatePicker to have text input format YYYY-MM-DD and Monday as first day of week?

I want my Flutter DatePicker to have text input format YYYY-MM-DD, and Monday as first day of week.

I'm using the code below to give the former:

var datePicked = await showDatePicker
(
    locale: const Locale('en', 'ZA'),
    ...

And I can use Locale('en', 'GB') to give the latter. But how do I do both at once please?

Sources

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