I’d like to add a custom admin field called ‘blurb’, right under the built-in field Description.
I realize my custom field can be in its own Options page, but having Site Title, Site Description, and Blurb all on one page is more intuitive.
I have the ACF Options Page addon. Can I use this to add a field to the WordPress Settings -> General page?
No, you would need to create a new options page under setting to store any custom options.
ACF does not have the ability to add fields to the standard options pages. You would need to stick to native WP functions
register_setting() does this, https://codex.wordpress.org/Function_Reference/register_setting and setting the $option_group to ‘general’ will add fields to this page. Unfortunately, I don’t think that even if you use this function that you can specify where the fields appear, I think they’ll all end up at the end.
