To see it in action:
Crust.piefed.social (the Piefed development instance)
Not all instances implement it yet, I guess it depends how often they pull from the dev branch
Example of search for 'movies'
You still don't see the number of weekly active users.
On Piefed, it's the 'Active people' column, where you can see the numbers without having to go to each community. Lemmy (and Photon in this case) only show subscribers, which isn't an accurate metric as most of them are ghost accounts.