Examples for default value in blueprints pages field

I am trying to specify a default value for a pages field in a blueprint, but I can’t find the proper way. Unless I missed something there is no example in the doc , I’d like to do something like this :

I am using Kirby 3.
Thanks

Since you are not dealing with an array, you can’t use the index…try first()

Thanks for your quick reply, unfortunately :
default: {{ site.children.filterBy('intendedTemplate', 'calculator').first() }}
does not work.
I also tried:
default: {{ first( site.children.filterBy('intendedTemplate', 'calculator') ) }}
both with and without curlybraces.

Instead, is there a way to just specify a uid as default value ? if yes, how to retrieve the uid of a page ?

Thanks

A path should work, e.g. in a Starterkit:

default: notes/across-the-ocean