How do I extract a JSON value if another value is higher than zero?

Question

My current code:

Powershell -Noprofile "(Get-Content 'allacts.txt' | ConvertFrom-Json).activityid | Out-File -FilePath ids%filenum%.txt"

This queries the JSON file (allacts.txt) and extracts a single value, activityid.

However, I don't want all the activityids, just the ones where the value attendedpeoplecount is higher than 0. How can I work that if logic into this command?

Sample:

[
  {
    "activityid": 610228,
    "attendedpeoplecount": 0
  },
  {
    "activityid": 568168,
    "attendedpeoplecount": 36
  }
]

Current command on the above json would return

610228
568168

The desired output would be

568168