Hi @julianbrada,
To hide this, simply add the following code snippet to your website:
.grimlock-buddypress-groups-section ul#groups-list.item-list>li div.item .item-meta .activity {
display: none !important;
}
To add this code snippet to your site, we recommend that you paste it to the Custom CSS panel of your WordPress Customizer. Just go to your dashboard and navigate to “Appearance > Customize > Additional CSS”.
Pasting your code snippet there should do the trick for you.
Regards,