Use case

DropdownButton is replaced by DropdownMenu with Material 3. DropdownButtonFormField should be replaced by a DropdownMenuFormField widget, but this one does not exists yet. It could be super useful to handle validator on DropdownMenu thanks to a FormField-dedicated widget.

Proposal

This should be a part of Flutter (as previous mentioned widgets). I tried to implement myself this new widget, but I figured out that there is too many obscure things I don't understand yet. Please find attached a very basic implementation, with a simple use
case (validator works, but there is a bug with the value not being changed).

demo.zip