Not built into core BuddyPress, but BuddyPress Activity Bump adds it as a free plugin. Worth knowing upfront how it actually works, because it’s automatic rather than manual: it isn’t a button you click to pin something, it bumps activity to the top of the stream automatically whenever someone likes or comments on it.
How It Works
Every new like or comment moves the parent activity back to the top of the feed. Practically, this means whatever’s getting engagement right now stays visible, and older posts that stop getting interaction drift back down naturally, no admin has to curate it.
A Real Staleness Flag
This one needs a stronger warning than most plugins in this series: the plugin’s own listing shows its last update was October 2023, tested only against BuddyPress v12.3.0. That’s old enough to genuinely test on staging before relying on it, it isn’t closed or removed from sale, but nearly three years without an update on a plugin that hooks into activity queries is a real compatibility risk with current BuddyPress releases, not a minor caveat.
If it doesn’t behave correctly on your version, a custom solution built around flagging specific activities and adjusting the activity query’s sort order is the fallback, though that requires PHP and BuddyPress development experience, or a developer to build it for you.