The most direct way is a switch you turn on while importing. You can also clean up prospects who've gone quiet after they're already in a campaign.
Filter as you import (easiest)
When you add prospects, turn on Only add prospects that posted in the last 30 days. Extrovert then adds only people who have posted recently and skips the quiet ones. This switch is available whichever way you add prospects.
Import from a Sales Navigator search
If you build your list in Sales Navigator, add a recent-post activity filter to your search before importing, so only active posters come through:
Open your Sales Navigator search
Set your target criteria (industry, role, location)
Add the recent-post activity filter
Paste the search URL into Extrovert to import
For all the import methods, see the complete guide to importing prospects.
Clean up prospects who stopped posting
Already imported people who don't post? On your prospect list, open the ... menu and choose Delete inactive prospects. This removes everyone who hasn't posted in the last 30 days, and it can't be undone.
Prefer to keep them? Instead of deleting non-posters, you can still reach them by engaging with posts they're likely to see.