[r-a-y]

Look into the Groups loop and adjust the parameters to output a list of group forums:

https://codex.buddypress.org/developer-docs/custom-buddypress-loops/the-groups-loop/

These are the parameters you should be looking at: “most-forum-topics” and “most-forum-posts”.

Copy /bp-themes/forums/index.php in a child theme and add a new groups loop.

This won’t make it look exactly like the forums here on bp.org, but will come close.