Hi,
I think I found a tiny bug in the documentation at https://getkirby.com/docs/reference/panel/blueprints/site#custom-preview-url.
title: Site
preview: https://mycustomdomain.com
does not work for me with kirby 3.3.2.
Instead, it works as specified in Page Preview:
title: Site
options
preview: https://mycustomdomain.com
Where would be the right place to report such a thing?