Sallyport Support

Click Sallyport's shield in the menu bar and turn on the switch at the top of the panel. The first time, macOS asks you to allow the network extension in System Settings → General → Login Items & Extensions, and then whether Sallyport may filter network content. Allow both.

Most likely a rule denies it, or Sallyport is in Silent — Deny mode. Open Connections (⌘L) from the menu bar to see which connections were blocked, then open Rules (⌘R) to change or delete the rule.

To check whether Sallyport is involved at all, turn the filter off for a moment with the switch at the top of the panel, and try again.

They decide what happens to a connection no rule covers. Alert asks you, Silent — Allow lets it through, and Silent — Deny blocks it.

In Alert mode, connections are allowed while the Sallyport app isn't running, because there's nobody to ask. macOS's own services are allowed in every mode unless you turn that off in Settings → Advanced.

After the waiting time (one minute unless you change it in Settings → Alerts), the connection is allowed or denied, as set under If there's no answer. While an alert is open, the app's new connections wait for your answer. UDP traffic, such as DNS or video calls, can't wait, so it's let through meanwhile.

Yes. In the Rules window, use Import & Export → Export Rules… to save them to a file, and Import Rules… on the other Mac. Rules that last only until an app quits aren't exported.

Choose Settings → Advanced → Uninstall… and pick whether to keep your rules for later. Sallyport removes its network extension and then offers to move itself to the Trash.

No. It looks at where connections go, not what they contain, and nothing leaves your Mac. The privacy policy has the details.