Exactly this…
There are posts on here from almost a decade ago which are asking for this feature.
I’ve seen replies about needing to make the plugin lightweight, in which case, can we have some kind of add on, or enable it with some configuration elsewhere?
You should probably rename page-ad to page_ad first
Then I think something like the following should work:
$group = get_field( 'page-ad', 'option );
$subHeading = $group['sub_heading'];
make a custom post type which is public and you should be fine.
You can use this generator to assist with that.
https://generatewp.com/post-type/