Thank you for the hint!
I managed to resolve it using the std option, like this:
$meta_boxes[] = [
'title' => 'My settings',
'id' => 'my_settings_id',
'settings_pages' => ['my_settings_page'],
'tab' => 'my_settings_tab',
'fields' => [
[
'name' => 'My field',
'id' => 'my_field_id',
'type' => 'text',
'std' => get_option( 'my_settings_id' )['my_field_id'],
'disabled' => true,
'save_field' => false,
],
]
]
So the value will never be saved to DB, and I'm able now to see the value of the same field safely.
.
