Hiding the subgroups on the group's directory page is not an available feature on our platform. One workaround that we can think of is by creating group types, then add the subgroups to them. 

Then look for the Permissions section and you can find an option to hide the groups that are listed on this group type. Please see the below image for your reference:


This sounds like it might be a great idea for a feature request or enhancement. You can share this on our new roadmap page. Head over to https://www.buddyboss.com/roadmap and click the "+" Submit idea button to suggest a new feature.