It would be very helpful if this list was sortable by recent activity so I could participate in recent discussions and help answer questions. I own too many games to keep track of all forums.
Currently the short list presented is not, and the long list(entire list) seems to be restricted to alphabetic option only.

This feature would make keeping track of new posts easier and would encourage activity in the game-specific subforums.

Can't hurt to vote for this in the community wishlist: https://www.gog.com/wishlist/site/option_to_sort_forums_by_last_post_instead_of_alphabetically

One thing that might help:

If you look at the list of game specific forums, any that have no new posts have been grayed out, so you can just look at the ones in your list that are highlighted. That's what I do, anyway.