BuddyPress.org

If you have created a child theme of bp-default theme:

1. copy over create.php file https://buddypress.trac.wordpress.org/browser/tags/1.5.4/bp-themes/bp-default/groups/create.php

2. open up create.php, and above line #99 add: ` `
and then after line #106 add: “
so that you, the Site/Super Admin can create hidden groups if you want to

In effect, the hidden group option would look like this now:
`
<input type="radio" name="group-status" value="hidden" checked=”checked” />

`

3. upload the file to your child-theme-folder/groups/create.php

What @mercime said together with filtering `groups_valid_status` to only return public and private should do the trick.