the Join button should only appear for public groups. 

Also if this group has pricing, then Join can appear but it would take the user to the pricing woocommerce page.

p.s : I think you've already reported a groups directory page issue in the app. So we'll need to check all the issues related to this. 

can you share sample credentials to check your site. 

Do you need the quiz fix to disable groups directory  ? 

add this to Customizer - Custom CSS

.vibebp-component-groups a.button.is-primary.new_mail{display:none;}