The comment on this variable suggests a depreciated hook:
/**
* Name of the event fired when altering initial values.
*
* @deprecated in address:8.x-1.5 and is removed from address:8.x-2.0. Use
* hook_field_widget_form_alter() to change the address #default_value.
*
* @Event
*
* @see
https://www.drupal.org/project/address/issues/2838457 →
*/
hook_field_widget_form_alter() should be altered to be hook_field_widget_single_element_form_alter as detailed here https://www.drupal.org/node/3180429 →
Closed: won't fix
1.12
Code