@EGCND - I am afraid there's no way to achieve this outcome in an automated way. The only automated way I know of is disabling activities on specific date-time (https://experienceleague.adobe.com/docs/target/using/activities/activity-settings.html)
A possible solution could be to use Adobe Target APIs using an automated script which runs regularly (say hourly), however that will work for visitors and not for page-views.
1. Run the reporting API for the specific activity (https://developers.adobetarget.com/api/#get-ab-performance-report)
2. Get the visitors for the activity after processing the response from step 1
3. If the visitor count from step 2 is more than your threshold then deactivate the activity using https://developers.adobetarget.com/api/#update-ab-activity
Let me know if you need any more information. All the best!
Regards
Rajneesh